Tap drill for each pitch
Tap this hole: 2.5 mm (0.0984 in). Bolt must pass (normal clearance): 3.6 mm.
| Thread | Tap drill | Clearance |
|---|---|---|
| M3 | 2.5 mm | 3.6 mm |
M3 tap drill size (M3 tap hole) is 2.5 mm exactly: 3.00 − 0.50. Tapping drill for M3 and tap drill for M3 are that same 2.5 mm hole. Close clearance 3.2 mm, normal 3.4 mm, loose 4.0 mm. In plastic, use a heat-set insert; a 2.5 mm tapped hole in ABS strips the first time someone overtightens.
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 3 mm
Pitch 0.5 mm
Tap drill 2.5 mm
Minor Ø 2.459 mm
M3 × 0.5 at a glance
Tap drill vs clearance hole
Tap this hole (then cut the thread): 2.5 mm. Bolt must pass (clearance): 3.6 mm normal. That is why “M3 × 0.5 drill size” can mean two different holes — this page lists both.
How we use this in the toolroom
We tap M3 in tool-steel stop plates and in aluminium covers. Below M4, a spiral-point tap and a proper tapping fluid matter more than the chart — the tap is easy to snap.
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.
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: M8 × 1.25, M10 × 1.5, M12 × 1.75, M6 × 1, M16 × 2, M4 × 0.7, M5 × 0.8, 1/4-20 UNC, 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.