A clearance hole lets a fastener pass through without cutting an internal thread. The following supplier-recommended values are relatively generous clearances, not a universal close-fit or ISO tolerance series.
| Bolt designation | Supplier clearance hole (mm) | Nominal diametral clearance (mm) |
|---|---|---|
| M2 | 2.6 | 0.6 |
| M2.5 | 3.1 | 0.6 |
| M3 | 3.6 | 0.6 |
| M4 | 4.8 | 0.8 |
| M5 | 5.8 | 0.8 |
| M6 | 7 | 1 |
| M8 | 10 | 2 |
| M10 | 12 | 2 |
| M12 | 15 | 3 |
Clearance is a functional choice
A larger through hole allows more assembly movement but reduces positional location by the bolt shank. It may also change washer support and the available material near an edge. Close, normal and large-clearance series are different choices; do not label a supplier chart as all three.
A fastener through hole is larger than the nominal fastener diameter. A cut-tap drill is smaller than the thread’s major diameter so material remains for thread formation. For example, a 7 mm through hole for an M6 bolt is not an M6 tapping hole.
Example: radial versus diametral clearance
For an ideal 6.00 mm shank in a 7.00 mm hole, diametral clearance is 1.00 mm and centered radial clearance is 0.50 mm. That does not automatically allow 1 mm of hole-center error in a multi-plate stack: fastener and hole size tolerances, the mating plate and pattern position all affect assembly.
When bolts must pass through several holes, analyze the complete pattern and datum scheme. If accurate location is required, consider the designed locating feature rather than asking ordinary clearance bolts to serve as precision dowels.
Drawing and shop checks
Specify the hole diameter and tolerance, edge condition, recess geometry if present, and any positional requirement. Check the actual fastener shank, head and washer dimensions. Coating buildup can reduce usable clearance; laser-cut taper or a burr can make a nominally adequate opening difficult to assemble.
Use this selected chart for initial layout only. The fastener standard, structural joint requirements and approved drawing govern final dimensions.
Why two clearance-hole charts can disagree
The first table uses selected Accu recommendations. TR Fastenings publishes a different recommended clearance column. Neither source should be silently relabeled as every close, normal or large-clearance series. This comparison makes the source choice visible.
| Thread | Accu recommendation, mm | TR recommendation, mm |
|---|---|---|
| M3 | 3.6 | 3.4 |
| M4 | 4.8 | 4.5 |
| M5 | 5.8 | 5.5 |
| M6 | 7.0 | 6.6 |
| M8 | 10.0 | 9.0 |
| M10 | 12.0 | 11.0 |
| M12 | 15.0 | 13.5 |
| M14 | 17.0 | 15.5 |
| M16 | 19.0 | 17.5 |
| M18 | 22.0 | 20.0 |
| M20 | 24.0 | 22.0 |
| M22 | 26.0 | 24.0 |
| M24 | 28.0 | 26.0 |
| M27 | 33.0 | 30.0 |
| M30 | 35.0 | 33.0 |
Source for the other column: Accu tapping and clearance reference. Values are recommendations from those named sources, not automatic drawing approvals.
For an ideal 6.00 mm shank, a 6.60 mm hole leaves 0.60 mm diametral clearance, while a 7.00 mm hole leaves 1.00 mm. The larger opening may ease assembly but gives more movement before the shank contacts the edge and changes washer support. Pattern-position tolerances can consume the available movement.
Select the requirement before the nearest drill
If the drawing calls out a specific diameter/tolerance or ISO 273 series, follow that requirement and its stated edition; do not replace it with either supplier column. If the drawing is silent, obtain a design decision about alignment, edge distance, washer bearing and coatings. Clearance bolts are not automatically precision locating features. Only then choose a tool and inspect the actual finished hole.
Content updated October 8, 2026. Sources and numerical examples are explained above; examples are not production test results. Editorial method · Report a correction.
References and verification
Original explanations and worked examples by MfgWorkbench. Sources below support the stated concepts or selected reference data; they do not certify every example or a production application.
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