M8 × 1.25 Thread Dimensions

Basic information

Designation

M8 x 1.25

Thread system

ISO Metric

Series

coarse

Standard

ISO 261

Basic profile

ISO 68-1 basic profile

Flank angle

60°

Dimensions

Major diameter

8 mm

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

0.767 mm

Recommended tap drill

Ø 6.75 mm

These figures follow the ISO 68-1 basic profile of ISO 261. A 60° basic profile uses a fundamental triangle height H = 0.866025 × P, with external minor diameter d₃ = d − 1.226869 × P and internal minor diameter D₁ = d − 1.082532 × P; the two differ because the external root is rounded while the internal crest is truncated. A 55° Whitworth profile uses H = 0.960491 × P and a thread height of 0.640327 × P. The recommended tap drill is given as nominal diameter minus pitch, which approximates 75% thread engagement — adjust it for tough materials or deep holes.

No specification in this database uses M8 × 1.25 yet.

Other pitches at the same 8 mm diameter — a fine pitch on a coarse diameter, or the reverse, is the usual substitution question.

Neighbouring sizes in ISO Metric.