threadsizes

M10 Tap Drill Size (M10 x 1.5)

ISO metric coarse · 1.5 mm pitch · ISO 261 / 965-1, class 6H

What size drill bit for a M10 tap?

8.5 mmmetric drill
0.3347inch
8.50mm
77%thread
No 8.5 mm drill? Use R (71%).

To scale section of the tapped hole

Section of a M10 x 1.5 tapped hole to scale: 8.5 mm (0.3347) drill, thread length 1.5 times the diameter. ⌀10 mm P 1.5 mm DRILL 8.5 mm Thread 1.5 × D +5 P drill
Drawn from the M10 x 1.5 basic profile. Hatched area is the part; the thread runs 1.5 × D and the drill goes 5 pitches deeper for a plug tap.

Drill options % of thread

Drill options for M10 x 1.5
DrillInchmmThread6H
8.4 mm 0.3307 8.40 82% ✓
Q 0.3320 8.43 80% ✓
8.5 mmUse 0.3347 8.50 77% ✓
8.6 mm 0.3386 8.60 72% ✓
R 0.3390 8.61 71% ✓
8.7 mm 0.3425 8.70 67% ✗
11/32" 0.3438 8.73 65% ✗
8.8 mm 0.3465 8.80 62% ✗
S 0.3480 8.84 60% ✗

By material Aluminum, brass, mild steel: 8.5 mm (77%) · Stainless, tool steel: 8.6 mm (72%)

75% (orange tick) is the usual target. Hard or gummy metals like stainless are often tapped at 60 to 65% to spare the tap; aluminum, brass and plastic take 75% or a little more. The last column checks the hole against the 6H minor diameter limits (8.38 mm to 8.68 mm).

M10 x 1.5 ISO 261, 965-1, class 6H

Major diameter10 mm / 0.3937 in
Pitch1.5 mm
Pitch diameter (basic)9.026 mm
Minor diameter 6H8.376–8.676 mm
Thread-forming tap drill9.3 mm 0.3661 in

Clearance hole ISO 273

Close10.5 mm10.5 mm
Normal11 mm11 mm
Loose12 mm12 mm

For a screw that passes through the part. Normal fit is the default; close fit locates the part more accurately but leaves no room for hole position error.

Hole depth rule of thumb

  • 10 mmthread length for full strength in steel (1 × D)
  • 15 mmin cast iron or brass (1.5 × D), up to 20 mm in aluminum
  • +7.5 mmextra drill depth below the thread for a plug tap (5 pitches), +3 mm with a bottoming tap

Shop notes

Plain "M10" is this thread, with a 1.5 mm pitch, and the drill is 8.5 mm for about 77% thread. M10 also comes in 1.25 mm and 1 mm fine pitches, each with its own drill, so it pays to know which one the part actually wants before drilling.

The window here is narrower than it looks. Everything from 8.4 mm to letter R (0.3390 in, 71%) passes the 6H minor diameter check; at 8.7 mm you are already outside it. For an inch shop the letter R is the drill to use, or a letter Q (0.3320 in, 80%) in soft material. The 11/32 that people reach for is outside the limits at 65%, so treat it as a last resort, not a substitute.

The same trap works in the other direction. The 8.8 mm drill belongs to M10 x 1.25, and in a coarse M10 hole it leaves 62% thread and fails the check.

The nearest inch thread is 3/8-16, which is smaller (0.375 in against 0.3937 in) and has a pitch of 1.5875 mm, not far from 1.5 mm. That near match is the problem: a 3/8-16 bolt can start in an M10 hole and only bind a few turns in, and forcing it past that point ruins both threads.