M8 × 1.25 tap drill size
Tap this hole: 6.8 mm (0.2677 in). Bolt must pass (normal clearance): 8.8 mm.
| Thread | Tap drill | Clearance |
|---|---|---|
| M8 | 6.8 mm | 8.8 mm |
| M8 × 1 | 7 mm | 8.8 mm |
| M8 × 0.75 | 7.3 mm | 8.8 mm |
M8 drill size is 6.8 mm when you are tapping M8 × 1.25, and 9.0 mm when the M8 bolt must pass (normal clearance). M8 × 1.25 thread dimensions: major Ø 8.00 mm, pitch 1.25 mm, tap drill 6.8 mm, minor Ø about 6.65 mm. What size drill bit for M8 × 1.25 tap: 6.8 mm (M8 tap drill bit size / M8 tapping drill size). Workshop tap drill for 75% engagement is major minus pitch: 8.00 − 1.25 = 6.75 mm, issued as 6.8 mm. Fine M8 × 1 uses 7.0 mm; M8 × 0.75 uses 7.3 mm (8.00 − 0.75, to 0.1 mm).
Common metric tap drills: M3 tap drill size · M6 tap drill 5.0 mm · M8 tap drill size · M10 tap drill 8.5 mm · M12 tap drill 10.2 mm · M24 tap drill 21.0 mm.
Formula
Major Ø 8 mm
Pitch 1.25 mm
Tap drill 6.8 mm
Minor Ø 6.647 mm
M8 × 1.25 at a glance
Tap drill vs clearance hole
Tap this hole (then cut the thread): 6.8 mm. Bolt must pass (clearance): 8.8 mm normal. That is why “M8 × 1.25 drill size” can mean two different holes — this page lists both.
How we use this in the toolroom
M8 is the default cover-screw and clamp size on our die sets. We tap 6.8 mm in steel, and in aluminium we often drop in a helical insert instead of trusting a 6.8 mm open hole.
Accurate Industries in Pune still looks these sizes up the same way: tap drill ≈ major − pitch, then a clearance hole for the bolt. AlwaysReach is that chart in the browser — our story.
Why the M8 cut-tap drill is 6.8 mm, how the major-minus-pitch rule rounds, and how a roll tap uses a larger hole, is written up in M8 tap drill size: why it is 6.8 mm. The number on this page stays the calculator result.
Full metric and imperial lookup lives on the thread & tap drill calculator. After tapping, check a locational bore on the ISO tolerance calculator. Other pages: M10 × 1.5, M12 × 1.75, M6 × 1, M16 × 2, M4 × 0.7, M5 × 0.8, 1/4-20 UNC, M3 × 0.5, M20 × 2.5, M24 × 3, 5/16-18 UNC, 3/8-16 UNC, 1/2-13 UNC, UNC chart, UNF chart, BSW chart, UNEF chart, BSF chart.