METRICcoarse60° flank

M20 × 2.5 Thread Dimensions

M20 x 2.5 is a coarse pitch METRIC thread. Pitch is 2.5 mm, equivalent to 10.16 threads per inch. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø20 mm
Pitch2.5 mm
Threads per inch10.16
Pitch Ø18.38 mm
Tap drill17.5 mm

Thread profile

millimetres unless stated
Thread profile — M20 x 2.5d 20d2 18.38d3 16.93mm60°P 2.5h3 1.53tap ⌀17.5
M20 × 2.5 — basic profile60° flank angle · Not to scale
Designation
M20 x 2.5
Thread system
METRIC
Series
coarse
Flank angle
60°
Major diameter
20 mm / 0.79"
Pitch
2.5 mm
Threads per inch
10.16
Pitch diameter
18.38 mm
Minor diameter (external)
16.93 mm
Minor diameter (internal)
17.29 mm
Thread depth
1.53 mm
Recommended tap drill
Ø 17.5 mm / 0.69"

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.