M27 × 2 tap drill size
The tap drill for M27×2 fine is 25 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% | 25.441 mm 1.0016" | 25.5 mm (58%) | 1" 1.0000" (62%) |
| 65% | 25.311 mm 0.9965" | 25.25 mm (67%) | 1" 1.0000" (62%) |
| 70% | 25.181 mm 0.9914" | 25.25 mm (67%) | 63/64" 0.9844" (77%) |
| 75% | 25.051 mm 0.9863" | 25 mm (77%) | 63/64" 0.9844" (77%) |
| 80% | 24.922 mm 0.9812" | 25 mm (77%) | 63/64" 0.9844" (77%) |
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 25.25 mm drill gives 67%. For mild steel, brass and cast iron the 25 mm is fine.
- At this size many people bore the hole and screwcut the thread on the lathe instead of using a hand tap. See the thread calculator for depths and the infeed.
- For a blind hole with 1.5 × D thread engagement (40.5 mm), drill about 48.5 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 M27 × 2
| Fit | Drill |
|---|---|
| Close | 28 mm (1.102") |
| Medium (normal) | 30 mm (1.181") |
| Free (loose) | 32 mm (1.260") |
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.
M27 × 2 thread data
| Designation | M27×2 fine |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 2 mm pitch (12.7 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 27 mm (1.063") |
| Pitch (effective) diameter | 25.701 mm (1.012") |
| Minor diameter, external | 24.546 mm (0.966") |
| Minor diameter, internal | 24.835 mm (0.978") |
| Thread depth (internal) | 1.083 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:
- 24.75 mm drill → about 87% thread
- 25 mm drill → about 77% thread
- 25.25 mm drill → about 67% thread
Other pitches of M27: M27 coarse.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M27 – 27 mm major, 3 mm pitch (8.5 TPI equivalent)
- G3/4 (3/4" BSP) – 26.44 mm major, 14 TPI (1.814 mm pitch)
- 1" UNC – 25.4 mm major, 8 TPI (3.175 mm pitch)
- 1" UNF – 25.4 mm major, 12 TPI (2.117 mm pitch)
- 1" BSW – 25.4 mm major, 8 TPI (3.175 mm pitch)
Questions
What size drill for a M27 × 2 tap?
The tap drill for M27×2 fine is 25 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M27 × 2?
For a M27 × 2 screw or bolt, drill 28 mm for a close fit, 30 mm for a medium (normal) fit or 32 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M27 × 2?
M27×2 fine has a 2 mm pitch (12.7 TPI equivalent), a 60° thread angle and a 27 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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