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Hole and Shaft Fits Explained: H7, H8, g6, h6 and Common CNC Fits
Views: 0 Author: NAITE TECH Engineering Team Publish Time: 2026-10-26 Origin: Site
Hole and shaft fits determine how two mating components assemble, move, and remain positioned relative to each other. For CNC machined parts, selecting the correct fit is essential for components such as precision shafts, bushings, locating pins, bearing housings, and mechanical assemblies.
ISO 286 provides a standardized system for specifying dimensional tolerances and fits. Common designations such as H7, H8, g6, and h6 define allowable hole or shaft dimensions, while combinations such as H7/g6 and H7/h6 establish the dimensional relationship between mating parts.
This guide explains how ISO 286 fits work, compares common tolerance classes, and demonstrates how to calculate clearance and interference using practical CNC machining examples. It also covers fit selection, manufacturing methods, and inspection requirements.
Quick Answer: H7 and H8 are hole tolerance classes, while g6 and h6 are shaft tolerance classes. The letter defines the tolerance zone relative to the nominal size, and the number identifies the tolerance grade. For example, a Ø25 mm H7/g6 fit provides a diametral clearance of 0.007–0.041 mm under ISO 286. The correct fit depends on whether the assembly needs movement, accurate location, or a secure interference connection.
What Are Hole and Shaft Fits?
A hole and shaft fit describes the dimensional relationship between two mating features with the same nominal size.
In a typical assembly, the hole is an internal cylindrical feature, while the shaft is the external cylindrical feature inserted into it.
Although both components may have a nominal diameter of 25 mm, they cannot be manufactured to one mathematically exact dimension. Each feature is produced within a specified range of acceptable sizes.
The relationship between these limits determines how the components assemble.
Clearance Fit
A clearance fit occurs when the minimum permitted hole size is greater than or equal to the maximum permitted shaft size.
This means the components have nonnegative diametral clearance at all permitted size combinations.
Clearance fits are commonly considered for applications such as:
Assemblies that require straightforward insertion and removal
The required amount of clearance depends on the function.
A sliding component may need enough space for smooth movement, lubrication, and thermal expansion. A locating component may require much smaller clearance to reduce unwanted movement.
A clearance fit does not automatically guarantee suitable running performance. Surface finish, alignment, load, lubrication, and operating temperature must also be considered.
Transition Fit
A transition fit allows either a small clearance or a small interference, depending on the actual dimensions of the manufactured components.
For example, a hole near its maximum limit and a shaft near its minimum limit may assemble with clearance.
A hole near its minimum limit and a shaft near its maximum limit may require a pressing force.
Transition fits are commonly evaluated when accurate location is important and the assembly does not necessarily require a large interference.
Typical applications include selected locating hubs, precision sleeves, and components requiring controlled positioning.
Interference Fit
An interference fit occurs when the minimum permitted shaft diameter exceeds the maximum permitted hole diameter.
The shaft is therefore larger than the hole throughout the specified tolerance ranges.
Assembly may require:
A controlled pressing operation
Heating the surrounding component
Cooling the shaft
A combination of thermal and mechanical assembly methods
Interference fits can help retain bushings, sleeves, and other cylindrical components without relying solely on separate fasteners.
However, interference must be evaluated against the material properties, wall thickness, contact pressure, assembly force, and operating loads.
An interference fit that works in a thick steel housing may be unsuitable for a thin-wall aluminum component.
Clearance, Transition and Interference Fits Compared
Fit type
Dimensional relationship
Typical functional purpose
Clearance fit
Hole is at least as large as shaft
Sliding, running, or removable assembly
Transition fit
Either clearance or interference is possible
Accurate positioning and controlled assembly
Interference fit
Shaft is always larger than hole
Secure retention and press-fit connections
The correct fit is determined by the application's functional requirements, not simply by choosing the smallest available tolerance.
Understanding ISO 286: H7, H8, g6 and h6
ISO 286 establishes a standardized system for specifying tolerances on linear sizes.
The two main references are:
ISO 286-1:2010: Defines the basic concepts of the ISO tolerance and fit system, including tolerance classes, deviations, and fits.
ISO 286-2:2010: Provides standard tolerance grades and limit deviations for commonly used hole and shaft tolerance classes.
As of October 2026, both standards remain current.
What Does H7 Mean?
The designation H7 has two parts:
H identifies the fundamental deviation and position of the hole tolerance zone.
7 identifies the International Tolerance grade, IT7, which determines the tolerance width for the relevant nominal size range.
For an H hole, the lower deviation is zero.
This means an H7 hole has a minimum permitted size equal to its nominal dimension.
For example, a Ø25 H7 hole has the following limits:
25.000–25.021 mm
The permissible variation is therefore 0 to +0.021 mm, not ±0.021 mm.
What Does H8 Mean?
H8 uses the same basic hole position as H7, but its IT8 tolerance grade provides a wider permissible size range.
For a nominal diameter of 25 mm:
H7: 25.000–25.021 mm
H8: 25.000–25.033 mm
Both have a zero lower deviation.
The difference is the width of their tolerance zones.
An H8 hole generally allows more dimensional variation than an H7 hole of the same nominal size.
However, this does not mean that H8 is automatically preferable for lower-cost manufacturing. The required fit and assembly function must still be considered.
What Does g6 Mean?
The lowercase letter g identifies a shaft tolerance zone located below the nominal size.
The number 6 identifies the IT6 tolerance grade.
For a nominal diameter of 25 mm, a g6 shaft has these limits:
24.980–24.993 mm
Its upper deviation is −0.007 mm, and its lower deviation is −0.020 mm.
The shaft is therefore always smaller than the nominal diameter within its permitted size range.
When combined with an H7 hole, it produces a positive clearance.
What Does h6 Mean?
For an h6 shaft, the upper deviation is zero.
The shaft's maximum permitted size is equal to its nominal dimension.
For a nominal diameter of 25 mm:
24.987–25.000 mm
Compared with g6, the h6 tolerance zone is positioned closer to the nominal size.
Both g6 and h6 use the IT6 grade for the same nominal size range, but their tolerance zones occupy different positions.
Important: g6 and h6 do not represent two different tolerance grades. They have the same grade number, but different fundamental deviations.
Hole-Basis and Shaft-Basis Systems
Two common approaches are used when selecting ISO fits.
Hole-basis system
The hole uses an H tolerance class, and the shaft tolerance class is selected to obtain the required fit.
Examples include:
H7/g6
H7/h6
H7/k6
H7/p6
This is a common approach when holes are manufactured using standard tooling or controlled finishing processes.
Shaft-basis system
The shaft uses an h tolerance class, while the hole tolerance class is selected according to the required fit.
This approach may be useful when a standard shaft size must be retained or when manufacturing and assembly constraints favor a fixed shaft tolerance zone.
Neither system is inherently superior for every application.
The selection should reflect component availability, manufacturing methods, fit requirements, and cost.
H7, H8, g6 and h6 Tolerance Chart
The actual dimensional limits for H7, H8, g6, and h6 depend on the nominal diameter.
A tolerance class does not represent one fixed deviation across all sizes.
For example, an H7 hole with a diameter of 10 mm has a different tolerance width from an H7 hole with a diameter of 50 mm.
ISO 286 Tolerance Reference for Ø25 mm
The following example applies to the nominal size range over 18 mm up to and including 30 mm.
Tolerance class
Lower deviation
Upper deviation
Actual size at Ø25 mm
H7 hole
0 µm
+21 µm
25.000–25.021 mm
H8 hole
0 µm
+33 µm
25.000–25.033 mm
g6 shaft
−20 µm
−7 µm
24.980–24.993 mm
h6 shaft
−13 µm
0 µm
24.987–25.000 mm
Reference: ISO 286-1:2010 and ISO 286-2:2010. Values are shown in micrometers (µm), with the corresponding limits in millimeters.
1 µm = 0.001 mm
For example, the upper deviation of +21 µm corresponds to +0.021 mm.
Therefore:
25.000 + 0.021 = 25.021 mm
This calculation establishes the upper size limit of a Ø25 H7 hole.
How H7 Tolerance Changes with Diameter
The following examples show why nominal diameter must be included when discussing H7 tolerances.
Nominal diameter
H7 deviation
H7 hole limits
Ø10 mm
0 / +15 µm
10.000–10.015 mm
Ø25 mm
0 / +21 µm
25.000–25.021 mm
Ø50 mm
0 / +25 µm
50.000–50.025 mm
These examples belong to different nominal size ranges under ISO 286.
The values for Ø25 mm cannot be applied to Ø50 mm without checking the corresponding standard table.
At a size-range boundary, use the correct interval. For example, a nominal diameter of exactly 30 mm belongs to the interval over 18 mm up to and including 30 mm.
H7 vs H8: Which Is More Accurate?
For the same nominal size, H7 has a narrower tolerance zone than H8.
At Ø25 mm:
H7 width: 21 µm
H8 width: 33 µm
An H7 hole consequently requires control within a narrower dimensional range.
However, this does not mean every H7 hole requires grinding or every H8 hole can be produced by ordinary drilling.
The appropriate machining route depends on the material, geometry, hole depth, required surface quality, and production process.
A tolerance designation specifies the acceptable finished size—not the manufacturing method.
g6 vs h6: What Is the Difference?
At Ø25 mm:
g6: 24.980–24.993 mm
h6: 24.987–25.000 mm
Both have a tolerance width of 13 µm.
The g6 zone lies farther below the nominal diameter, while the h6 zone reaches the nominal dimension at its upper limit.
This difference changes the resulting clearance when either shaft is assembled with the same H7 hole.
For complete limits, other tolerance classes, and additional nominal size ranges, consult the applicable ISO 286-2 standard.
Common Hole and Shaft Fits Compared
Several ISO hole-basis fit combinations are commonly used in mechanical design.
The best selection depends on whether the components must move freely, locate accurately, or remain firmly connected.
Common ISO 286 Fit Combinations
Fit designation
General fit category
Typical application considerations
H8/f7
Clearance
Running or sliding applications requiring additional clearance
H7/g6
Clearance
Controlled sliding and precision guiding
H7/h6
Clearance, potentially zero
Accurate removable location
H7/k6
Transition
Close location with possible light interference
H7/n6
Transition
Tighter location with possible interference
H7/p6
Interference for the Ø25 mm example
Press-fit sleeves or retained cylindrical components
H7/s6
Interference
More demanding interference connections
Fit categories and example applications are general engineering guidance. Verify the actual clearance or interference at the intended nominal diameter and against the assembly requirements.
H7/g6: Clearance Fit for Controlled Movement
H7/g6 provides positive diametral clearance.
It is frequently considered for precision sliding applications where the shaft must move relative to the hole or bushing.
Potential applications include:
Guide shafts
Sliding mechanisms
Removable precision sleeves
Components requiring controlled radial clearance
However, H7/g6 should not automatically be selected for every rotating shaft.
Rotational speed, load, lubrication, operating temperature, and surface condition may require a different fit.
H7/h6: Close Locating Clearance Fit
H7/h6 is commonly associated with precise removable location.
The maximum shaft size equals the nominal diameter, while the minimum H7 hole size also equals the nominal diameter.
Consequently, the minimum calculated diametral clearance is zero.
This makes it suitable for applications where components need relatively close dimensional location without a specified interference throughout the tolerance range.
However, zero calculated clearance does not guarantee easy hand assembly.
Actual shape errors, surface condition, measurement uncertainty, and thermal conditions can affect assembly behavior.
H7/k6 and H7/n6: Transition Fits
These combinations can produce either clearance or interference, depending on the actual manufactured sizes.
They may be considered for components requiring closer positional control than a conventional clearance fit.
Assembly force and disassembly requirements should be evaluated before selecting them.
For example, a transition fit may be appropriate for a locating sleeve, but unsuitable for a component that must slide repeatedly during normal operation.
H7/p6 and H7/s6: Interference Fits
These combinations are used where a secure connection is required through interference.
Potential applications include selected press-fit bushings, hubs, and sleeves.
The interference must be sufficient to provide the intended retention without overstressing the components.
For press-fit applications, consider:
Material strength and elastic modulus
Shaft and housing diameter
Housing wall thickness
Contact length
Required axial or torsional load
Assembly method
Operating temperature
A fit designation is a starting point for engineering design. It does not replace an interference-pressure or structural assessment.
Worked Example: Calculating a Ø25 H7/g6 Fit
Consider a hypothetical assembly consisting of a precision shaft installed into a machined cylindrical bore.
The engineering drawing specifies:
Ø25 H7/g6
The nominal diameter is 25 mm.
The hole uses H7, and the shaft uses g6.
The objective is to calculate the smallest and largest possible diametral clearance.
This is an illustrative calculation based on ISO 286, not an actual NAITE TECH customer project or inspection result.
Step 1: Determine the H7 Hole Limits
For the nominal size range over 18 mm up to and including 30 mm:
H7 lower deviation = 0 mm
H7 upper deviation = +0.021 mm
Therefore:
Minimum hole diameter = 25.000 mm
Maximum hole diameter = 25.021 mm
Step 2: Determine the g6 Shaft Limits
For the same nominal size range:
g6 upper deviation = −0.007 mm
g6 lower deviation = −0.020 mm
Therefore:
Maximum shaft diameter = 24.993 mm
Minimum shaft diameter = 24.980 mm
Step 3: Calculate Minimum Clearance
Minimum Clearance = Minimum Hole − Maximum Shaft
Minimum diametral clearance occurs when the hole is at its smallest permitted size and the shaft is at its largest permitted size.
25.000 − 24.993 = 0.007 mm
Therefore, the minimum diametral clearance is:
7 µm
Step 4: Calculate Maximum Clearance
Maximum diametral clearance occurs when the hole is at its largest permitted size and the shaft is at its smallest permitted size.
Maximum Clearance = Maximum Hole − Minimum Shaft
25.021 − 24.980 = 0.041 mm
Therefore, the maximum diametral clearance is:
41 µm
Ø25 H7/g6 Fit Calculation Summary
Parameter
Calculated result
Nominal diameter
25 mm
Hole tolerance
H7
Hole limits
25.000–25.021 mm
Shaft tolerance
g6
Shaft limits
24.980–24.993 mm
Minimum diametral clearance
0.007 mm
Maximum diametral clearance
0.041 mm
Fit classification
Clearance fit
This combination always produces positive theoretical diametral clearance when the hole and shaft sizes are within their specified limits.
What Happens If We Change the Shaft Tolerance?
Keeping the same Ø25 H7 hole, the resulting fit changes when the shaft tolerance class changes.
Fit
Minimum clearance
Maximum clearance
Classification
H7/g6
+0.007 mm
+0.041 mm
Clearance
H7/h6
0 mm
+0.034 mm
Clearance, zero minimum
H7/k6
−0.015 mm
+0.019 mm
Transition
H7/p6
−0.035 mm
−0.001 mm
Interference
Calculated using representative ISO 286 limit deviations for a nominal diameter of 25 mm. Negative clearance indicates interference.
These values illustrate why changing only one letter can change the assembly behavior significantly.
For H7/k6, the assembly may have up to 0.019 mm clearance or up to 0.015 mm interference.
For H7/p6, the shaft is always larger than the hole within the permitted size limits, with a calculated diametral interference of 0.001–0.035 mm.
These are dimensional relationships, not guaranteed insertion forces or retention capacities.
Actual assembly performance also depends on form, surface condition, material behavior, and operating conditions.
ISO 286 Fit Calculator | Embedded Widget | NAITE TECH
Reference range: over 18 mm, up to and including 30 mm.
Tolerance Zone DiagramDeviations from nominal · µm
Hole Shaft Nominal zero line
Minimum difference = minimum hole − maximum shaft. Maximum difference = maximum hole − minimum shaft. Positive means diametral clearance; negative means interference.
Engineering reference only. The selected ISO 286-1/-2:2010 deviations and calculated fits must be verified against the applicable controlled standard and approved drawing before production use. Dimensions and clearance values are diametral, not radial.
FREE ENGINEERING TOOL
Calculate Your Hole and Shaft Fit
Calculate ISO 286 hole and shaft limits, minimum and maximum diametral differences, and clearance, transition or interference fits using our online calculator.
Choosing a fit begins with the intended function of the assembly.
Engineers should not select a tolerance combination simply because it appears frequently in a reference chart.
The first question is:
What must the two components do when assembled?
For Sliding or Rotating Components
Where movement is required, start by evaluating suitable clearance fits.
The required clearance should consider:
Operating speed
Radial loading
Lubrication
Expected temperature range
Surface finish
Shaft and hole alignment
Wear and service life
A guide shaft with intermittent movement may have very different requirements from a continuously rotating journal.
A small clearance is not always better.
Insufficient clearance may cause binding, particularly when thermal expansion, misalignment, or surface variation is present.
For Precision Location and Removable Assembly
When accurate positioning is more important than continuous movement, a close clearance or transition fit may be appropriate.
Examples include:
Locating sleeves
Removable positioning shafts
Alignment components
Certain dowel and fixture assemblies
The designer should determine whether the assembly must be removable by hand, require light pressing, or remain installed for its entire service life.
This decision affects the fit selection.
For purchased locating pins, standardized bushings, and precision dowels, check the component manufacturer's dimensional specifications before choosing the mating bore.
For Press-Fit and Retained Components
Where the connection relies on interference, the required retention should be calculated rather than assumed.
The correct interference depends on contact pressure and the ability of the materials to sustain it.
For example, a steel bushing installed into an aluminum housing may require particular attention to:
Relative thermal expansion
Housing wall thickness
Risk of permanent deformation
Operating temperature
Required retention force
An interference fit that appears satisfactory at room temperature may change under operating conditions.
For critical assemblies, engineering calculations and appropriate validation testing should confirm the selection.
Consider Material and Temperature
Different materials expand by different amounts when temperature changes.
An aluminum housing and a steel shaft may therefore experience a change in clearance during heating or cooling.
The final fit must be suitable for the expected operating environment, not just the inspection room temperature.
Corrosion, wear, coatings, and repeated assembly can also alter functional behavior.
Consider Surface Finish and Geometric Accuracy
Even if the hole and shaft diameters meet ISO 286 limits, assembly may still be affected by:
Out-of-roundness
Cylindricity error
Taper
Misalignment
Surface roughness
Burrs and edge damage
For example, a shaft measured within its permitted diameter range may still cause local interference if its form is unacceptable for the intended function.
When necessary, specify additional form, orientation, or location requirements on the engineering drawing.
Fit tolerances should be treated as one part of a complete dimensional and geometrical specification.
Manufacturing parts with ISO 286 fits requires suitable process planning and dimensional verification.
An H7 hole or g6 shaft may involve a relatively narrow permissible size range, but the machining process depends on more than the tolerance designation.
Material, feature length, accessibility, rigidity, and production quantity all influence the manufacturing route.
CNC Turning for Precision Shafts
CNC turning is commonly used to produce rotational components such as:
Precision shafts
Pins
Bushings
Sleeves
Spacers
Stepped cylindrical components
For shaft tolerance classes such as g6 and h6, the manufacturer must consider tool wear, temperature, machine condition, and workholding.
The process may use controlled finish turning or additional finishing operations when required.
A shaft's diameter is only one aspect of its functional quality.
Long shafts may also require control of straightness, circularity, or other geometric characteristics.
H7 and H8 holes can be produced using different machining strategies.
Depending on the application, these may include:
Drilling followed by reaming
Precision boring
Fine boring
Suitable finishing operations
Grinding or honing where justified
The best process depends on the hole diameter, depth, material, geometry, required surface condition, and production volume.
An H7 designation does not require reaming by definition.
Reaming is one possible manufacturing process. A suitable boring or other finishing process may also achieve the required result.
Likewise, a conventional drilled hole should not be assumed to meet H8 or H7 without verification.
How to Inspect Hole and Shaft Tolerances
Precision-fit inspection should confirm that the manufactured components satisfy the specified size limits and any additional geometrical requirements.
Feature
Possible inspection method
Main consideration
Shaft diameter
Outside micrometer
Suitable measurement range and resolution
Precision bore
Bore gauge or internal micrometer
Bore size and measurement location
Hole-size acceptance
Appropriate plug gauge
Functional limit verification where suitable
Shaft-size acceptance
Appropriate ring or snap gauge
Functional limit verification where suitable
Hole location
CMM
Datum alignment and location requirements
Form characteristics
Roundness equipment or suitable CMM method
Measurement strategy and uncertainty
Surface roughness
Profilometer
Specified surface texture
The exact inspection method should be selected according to the characteristic being measured.
A general-purpose caliper may be useful for many CNC dimensions but may not provide adequate measurement capability for every small ISO fit tolerance.
Measurement uncertainty, temperature, gauge calibration, and repeatability should be considered when evaluating dimensional conformity.
Does a CMM Replace Bore Gauges?
Not necessarily.
A coordinate measuring machine can help evaluate dimensional and geometrical characteristics, especially where multiple features or datum relationships must be verified.
However, a suitable bore gauge or other dedicated instrument may be more effective for some precision diameter checks.
Instrument choice should depend on the tolerance, feature geometry, measurement strategy, and available measurement capability.
Even when engineers use standard ISO tolerance designations, manufacturing or assembly problems can occur if the requirements are incomplete.
The following mistakes are worth checking before releasing a drawing for CNC production.
1. Assuming H7 Means ±0.007 mm
H7 is not a universal ± tolerance.
The actual permissible deviation depends on the nominal size range.
For Ø25 H7, the deviation is 0 to +0.021 mm.
Always check the correct ISO 286 table before assigning dimensional limits.
2. Treating g6 and h6 as Different IT Grades
Both use IT6.
The difference is their tolerance-zone position relative to the nominal dimension.
Selecting g6 instead of h6 can change the resulting clearance even when the tolerance widths are equal.
3. Choosing a Fit Without Calculating Its Limits
A designation such as H7/k6 does not describe one fixed assembly condition without reference to the nominal diameter.
Calculate the minimum and maximum clearance or interference before finalizing the fit.
4. Using Clearance Fits Without Considering Operating Conditions
A clearance fit that is acceptable at room temperature may become unsuitable due to thermal expansion, lubrication requirements, or alignment errors.
Verify the intended operating environment.
5. Selecting Excessive Interference
A tighter interference fit does not always produce a better assembly.
Excessive interference can increase assembly force and may damage thin-wall components or cause permanent deformation.
Determine the required retention and evaluate the resulting stress.
6. Ignoring Form and Location Errors
A hole and shaft can satisfy their size limits while still having unacceptable geometric errors.
Specify roundness, cylindricity, alignment, or other geometric requirements where they affect function.
7. Forgetting Surface Treatments
Plating, coating, and other finishing processes may change final dimensions.
If the specified fit must be achieved after finishing, the drawing and process plan should make that requirement clear.
8. Not Defining the Inspection Method
A tight dimensional requirement without an appropriate measurement strategy can lead to disputes over conformity.
Confirm the inspection method, acceptance criteria, and documentation before production.
Hole and Shaft Fit Drawing Checklist
Before sending a drawing to a CNC manufacturer, verify the following information.
Requirement
What to confirm
Nominal diameter
Correct size and units
Hole tolerance
H7, H8, or another specified class
Shaft tolerance
g6, h6, k6, p6, or another selected class
Applicable standard
ISO 286 edition or agreed specification
Functional requirement
Sliding, locating, rotating, or retention
Material
Grade and condition of both components
Surface finish
Functional surface texture and treatments
Geometric requirements
Form, orientation, and location where needed
Inspection
Measurement method and reporting requirements
Assembly conditions
Temperature, load, lubrication, and installation method
A complete drawing helps the manufacturing supplier understand not only the required dimensions but also the purpose of the fit.
Frequently Asked Questions About Hole and Shaft Fits
What does H7 mean on an engineering drawing?
H7 is an ISO 286 hole tolerance class. The letter H places the lower deviation at zero, while the number 7 identifies the IT7 tolerance grade. The numerical size limits depend on the nominal diameter. For example, a Ø25 H7 hole has an acceptable diameter range of 25.000–25.021 mm.
What is the difference between H7 and H8?
H7 and H8 are both hole tolerance classes with a zero lower deviation. H8 provides a wider permissible size range than H7 at the same nominal diameter. At Ø25 mm, H7 permits 25.000–25.021 mm, while H8 permits 25.000–25.033 mm.
What is the difference between g6 and h6?
Both are shaft tolerance classes with IT6 tolerance width, but their zones occupy different positions. The g6 zone lies below the nominal dimension, while an h6 shaft has an upper deviation of zero. This changes the clearance when assembled with a given hole.
What is the clearance for a 25 mm H7/g6 fit?
For a nominal diameter of 25 mm, the H7 hole limits are 25.000–25.021 mm and the g6 shaft limits are 24.980–24.993 mm. The minimum diametral clearance is 0.007 mm, and the maximum is 0.041 mm.
Is H7/h6 a clearance fit or a transition fit?
H7/h6 is a clearance fit with a theoretical minimum diametral clearance of zero. At Ø25 mm, the maximum clearance is 0.034 mm. In practice, assembly also depends on surface condition, form, temperature, and measurement uncertainty.
Which ISO fit is commonly used for sliding shafts?
H7/g6 is one commonly considered clearance fit for controlled sliding applications. However, the correct selection depends on the required movement, load, lubrication, temperature, surface finish, and other assembly conditions. No single fit is appropriate for every sliding mechanism.
What is the difference between H7/k6 and H7/p6?
H7/k6 is a transition fit that can produce either clearance or interference. At Ø25 mm, H7/p6 is an interference fit, with a calculated diametral interference of 0.001–0.035 mm. The appropriate choice depends on the assembly's positioning, retention, and loading requirements.
Does an H7 hole require reaming?
No. H7 specifies a permissible hole-size range rather than a required machining method. Reaming, precision boring, and other suitable processes may achieve the tolerance depending on the material, geometry, and equipment. Final inspection is necessary to verify conformity.
Final Takeaway: Specify Fits Before CNC Manufacturing
Hole and shaft fits are fundamental to the function and interchangeability of precision mechanical assemblies.
ISO 286 provides a consistent way to specify allowable dimensional variation using tolerance classes such as H7, H8, g6, and h6.
However, choosing the correct fit requires more than identifying a familiar designation.
The designer must consider the required movement, positioning accuracy, retention, materials, operating conditions, machining process, and inspection method.
The key principles are:
Understand the notation. The letter identifies the tolerance-zone position, while the number defines the tolerance grade.
Calculate actual size limits. ISO tolerance deviations depend on the nominal diameter.
Choose fits according to function. Clearance, transition, and interference fits solve different assembly requirements.
Specify critical geometry. Diameter tolerance alone may not establish acceptable form, alignment, or location.
Confirm manufacturing and inspection requirements. The machining route and measurement plan should support the intended function.
A well-defined fit specification helps reduce uncertainty during quotation, manufacturing, inspection, and assembly.
Need Precision CNC Parts with Specified Hole and Shaft Fits?
NAITE TECH provides custom CNC machining services for precision shafts, bushings, sleeves, housings, and other drawing-based mechanical components.
With in-house CNC turning, Swiss-type machining, and dimensional inspection capabilities, we support projects ranging from prototypes to repeat production.
Our team can review the fit requirements shown on your engineering drawings and evaluate suitable manufacturing and inspection approaches.
Technical reference status reviewed: October 23, 2026.
The numerical tables are selected reference examples, not a reproduction of the complete ISO 286 standards. They are intended to explain the principles of dimensional fits and should be verified against the applicable controlled standard and approved drawing for production use.
Fit applications described in this guide are general engineering examples. Final fit selection, assembly design, and inspection requirements remain dependent on the specific product, materials, operating conditions, and contractual specifications.
