M8 × 1 tap drill size
The tap drill for M8×1 fine is 7 mm. That’s the standard chart size and gives about 77% of full thread.
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Tap drill by thread percentage
75% is the usual workshop figure. Less thread is easier to tap; more adds little strength.
| Thread % | Ideal drill | Nearest metric drill | Nearest imperial drill |
|---|---|---|---|
| 60% | 7.221 mm 0.2843" | 7.2 mm (62%) | 9/32" 0.2813" (66%) |
| 65% | 7.156 mm 0.2817" | 7.2 mm (62%) | 9/32" 0.2813" (66%) |
| 70% | 7.091 mm 0.2792" | 7.1 mm (69%) | letter K 0.2810" (66%) |
| 75% | 7.026 mm 0.2766" | 7 mm (77%) | letter J 0.2770" (74%) |
| 80% | 6.961 mm 0.2740" | 7 mm (77%) | letter I 0.2720" (84%) |
About this size
Fine-pitch metric threads are used where you need more strength in thin walls, finer adjustment or better resistance to vibration, for example on hydraulic and automotive parts. The pitch must be written in full (M10 × 1.25); without it, M10 means coarse.
- For stainless steel, duplex and other tough materials, go to about 65% thread: a 7.2 mm drill gives 62%. For mild steel, brass and cast iron the 7 mm is fine.
- For a blind hole with 1.5 × D thread engagement (12 mm), drill about 16 mm deep. That leaves room for the 3–4 tapered lead threads on a second or plug tap. In steel, 1 × D engagement is usually enough; in aluminium or cast iron allow 1.5–2 × D.
Clearance holes for M8 × 1
| Fit | Drill |
|---|---|
| Close | 8.4 mm (0.331") |
| Medium (normal) | 9 mm (0.354") |
| Free (loose) | 10 mm (0.394") |
Fine, medium and coarse series from ISO 273. Medium suits most jobs; use fine where parts must locate closely and coarse for quick assembly or coated bolts.
M8 × 1 thread data
| Designation | M8×1 fine |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 1 mm pitch (25.4 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 8 mm (0.315") |
| Pitch (effective) diameter | 7.35 mm (0.289") |
| Minor diameter, external | 6.773 mm (0.267") |
| Minor diameter, internal | 6.917 mm (0.272") |
| Thread depth (internal) | 0.541 mm |
Basic sizes. Real screws are slightly under and real nuts slightly over these values because of tolerance classes.
Quick calculator
Nearest alternatives
If you don’t have the right drill, these give:
- 6.9 mm drill → about 85% thread
- 7 mm drill → about 77% thread
- 7.1 mm drill → about 69% thread
Other pitches of M8: M8 coarse.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M8 – 8 mm major, 1.25 mm pitch (20.3 TPI equivalent)
- 5/16" UNC – 7.94 mm major, 18 TPI (1.411 mm pitch)
- 5/16" UNF – 7.94 mm major, 24 TPI (1.058 mm pitch)
- 5/16" BSW – 7.94 mm major, 18 TPI (1.411 mm pitch)
- 5/16" BSF – 7.94 mm major, 22 TPI (1.155 mm pitch)
Questions
What size drill for a M8 × 1 tap?
The tap drill for M8×1 fine is 7 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M8 × 1?
For a M8 × 1 screw or bolt, drill 8.4 mm for a close fit, 9 mm for a medium (normal) fit or 10 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M8 × 1?
M8×1 fine has a 1 mm pitch (25.4 TPI equivalent), a 60° thread angle and a 8 mm major diameter.
Sources: Chart drill: the usual fine-pitch rule, drill = D − P. Percent values from the ISO 68-1 basic profile. Clearance holes: ISO 273 (checked 25/10/2026). Values are for reference only – check your tap maker’s chart. See the disclaimer.
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