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Category: clearance holes
Reference Dataset
Metric Fastener Clearance Drill Sizing Table
Standard drill sizes for close, normal, and loose fit clearance holes for metric fasteners M3 to M20.
Overview & Scope
Clearance holes provide passing clearances for threaded fastener bolts to prevent interference with thread crests. Standards define close, normal, and loose fits depending on assembly tolerances.
Technical Sizing Values
The table below specifies recommended clearance drill sizes for metric fasteners M3 to M20.
| Fastener Size | Close Fit (mm) | Close Fit (in) | Normal Fit (mm) | Normal Fit (in) | Loose Fit (mm) | Loose Fit (in) |
|---|---|---|---|---|---|---|
| M3 | 3.2 | 0.126 | 3.4 | 0.134 | 3.6 | 0.142 |
| M4 | 4.3 | 0.169 | 4.5 | 0.177 | 4.8 | 0.189 |
| M5 | 5.3 | 0.209 | 5.5 | 0.217 | 5.8 | 0.228 |
| M6 | 6.4 | 0.252 | 6.6 | 0.26 | 7 | 0.276 |
| M8 | 8.4 | 0.331 | 9 | 0.354 | 10 | 0.394 |
| M10 | 10.5 | 0.413 | 11 | 0.433 | 12 | 0.472 |
| M12 | 13 | 0.512 | 14 | 0.551 | 15 | 0.591 |
| M16 | 17 | 0.669 | 18 | 0.709 | 19 | 0.748 |
| M20 | 21 | 0.827 | 22 | 0.866 | 24 | 0.945 |
Engineering Notes & Best Practices
- •Close fit is specified for critical alignments where assembly shift must be minimized.
- •Normal fit is the standard selection for general mechanical manufacturing and structures.
- •Loose fit accommodates large tolerances, stamping variations, or multi-plate stackups.
Dataset Citations & References
ASME B18.2.8 Clearance Holes for Bolt/Screw
Public domain source and standard catalog reference parameters.