METRICcoarse60° flank

M8 × 1.25 Thread Dimensions

M8 x 1.25 is a coarse pitch METRIC thread. Pitch is 1.25 mm, equivalent to 20.32 threads per inch. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø8 mm
Pitch1.25 mm
Threads per inch20.32
Pitch Ø7.19 mm
Tap drill6.75 mm

Thread profile

millimetres unless stated
Thread profile — M8 x 1.25d 8d2 7.19d3 6.47mm60°P 1.25h3 0.77tap ⌀6.75
M8 × 1.25 — basic profile60° flank angle · Not to scale
Designation
M8 x 1.25
Thread system
METRIC
Series
coarse
Flank angle
60°
Major diameter
8 mm / 0.31"
Pitch
1.25 mm
Threads per inch
20.32
Pitch diameter
7.19 mm
Minor diameter (external)
6.47 mm
Minor diameter (internal)
6.65 mm
Thread depth
0.77 mm
Recommended tap drill
Ø 6.75 mm / 0.27"

How these values are derived

Basic ISO thread geometry uses the fundamental triangle height H = 0.866025 × P. External minor diameter d₃ = d − 1.226869 × P, internal minor diameter D₁ = d − 1.082532 × P. Tap drill is given as nominal diameter minus pitch, which approximates a 75% thread engagement — adjust for tough materials or deep holes.