M2.5 tap drill size
The tap drill for M2.5×0.45 is 2.05 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% | 2.149 mm 0.0846" | 2.15 mm (60%) | #44 0.0860" (54%) |
| 65% | 2.12 mm 0.0835" | 2.1 mm (68%) | #45 0.0820" (71%) |
| 70% | 2.091 mm 0.0823" | 2.1 mm (68%) | #45 0.0820" (71%) |
| 75% | 2.062 mm 0.0812" | 2.05 mm (77%) | #46 0.0810" (76%) |
| 80% | 2.032 mm 0.0800" | 2.05 mm (77%) | #46 0.0810" (76%) |
About this size
ISO metric coarse is the default thread for general engineering in the UK and Europe. If a drawing just says “M10”, it means the coarse pitch.
- Taps this small snap easily. By hand, or in stainless steel, a 2.1 mm drill (about 68% thread) makes tapping much easier for very little loss of strength.
- For a blind hole with 1.5 × D thread engagement (3.8 mm), drill about 5.5 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 M2.5
| Fit | Drill |
|---|---|
| Close | 2.7 mm (0.106") |
| Medium (normal) | 2.9 mm (0.114") |
| Free (loose) | 3.1 mm (0.122") |
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.
M2.5 thread data
| Designation | M2.5×0.45 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 0.45 mm pitch (56.4 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 2.5 mm (0.098") |
| Pitch (effective) diameter | 2.208 mm (0.087") |
| Minor diameter, external | 1.948 mm (0.077") |
| Minor diameter, internal | 2.013 mm (0.079") |
| Thread depth (internal) | 0.244 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:
- 2 mm drill → about 86% thread
- 2.05 mm drill → about 77% thread
- 2.1 mm drill → about 68% thread
Threads close in size (not interchangeable – the pitch and/or angle differ):
- 7BA – 2.5 mm major, 0.48 mm pitch (52.9 TPI equivalent)
Questions
What size drill for a M2.5 tap?
The tap drill for M2.5×0.45 is 2.05 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M2.5?
For a M2.5 screw or bolt, drill 2.7 mm for a close fit, 2.9 mm for a medium (normal) fit or 3.1 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M2.5?
M2.5×0.45 has a 0.45 mm pitch (56.4 TPI equivalent), a 60° thread angle and a 2.5 mm major diameter.
Sources: Chart drill: the common metric coarse tapping chart. Percent values worked out 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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