METRICcoarse60° flankISO 261

M20 × 2.5 Thread Dimensions

M20 x 2.5 is a coarse ISO Metric thread. Pitch is 2.5 mm, equivalent to 10.16 threads per inch. The recommended tap drill is nominal diameter minus pitch.

Major 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 1.534tap ⌀17.5
M20 × 2.5 — basic profile60° flank angle · Not to scale

Basic information

Designation
M20 x 2.5
Thread system
ISO Metric
Series
coarse
Standard
ISO 261
Basic profile
ISO 68-1 basic profile
Flank angle
60°

Dimensions

Major diameter
20 mm
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
1.534 mm
Recommended tap drill
Ø 17.5 mm

How these values are derived

computed from the basic profile

These figures follow the ISO 68-1 basic profile of ISO 261. A 60° basic profile has a fundamental triangle height H = 0.866025 × P, with pitch diameter d₂ = d − 0.649519 × P, external minor diameter d₃ = d − 1.226869 × P and internal minor diameter D₁ = d − 1.082532 × P; the two minor diameters differ because the external root is rounded while the internal crest is truncated. The recommended tap drill is given as nominal diameter minus pitch, which approximates 75% thread engagement — adjust it for tough materials or deep holes.

Compatible parts74 specification pages

All M20 fasteners

Every fastener below is threaded M20 × 2.5, so a nut, bolt or washer picked from this list will mate with it.

DIN 912ISO 4762DIN 7991ISO 10642DIN 933ISO 4017DIN 931ISO 4014DIN 934ISO 4032DIN 439ISO 4035DIN 985ISO 10511ISO 4161DIN 6923
SpecificationLength
DIN 912 M20 × 30 Hexagon Socket Head Cap Screw30 mm
DIN 912 M20 × 35 Hexagon Socket Head Cap Screw35 mm
DIN 912 M20 × 40 Hexagon Socket Head Cap Screw40 mm
DIN 912 M20 × 50 Hexagon Socket Head Cap Screw50 mm
DIN 912 M20 × 60 Hexagon Socket Head Cap Screw60 mm
DIN 912 M20 × 80 Hexagon Socket Head Cap Screw80 mm
DIN 912 M20 × 100 Hexagon Socket Head Cap Screw100 mm
ISO 4762 M20 × 30 Hexagon Socket Head Cap Screw30 mm
ISO 4762 M20 × 35 Hexagon Socket Head Cap Screw35 mm
ISO 4762 M20 × 40 Hexagon Socket Head Cap Screw40 mm
ISO 4762 M20 × 50 Hexagon Socket Head Cap Screw50 mm
ISO 4762 M20 × 60 Hexagon Socket Head Cap Screw60 mm
ISO 4762 M20 × 80 Hexagon Socket Head Cap Screw80 mm
ISO 4762 M20 × 100 Hexagon Socket Head Cap Screw100 mm
DIN 7991 M20 × 30 Hexagon Socket Countersunk Head Screw30 mm
DIN 7991 M20 × 35 Hexagon Socket Countersunk Head Screw35 mm
DIN 7991 M20 × 40 Hexagon Socket Countersunk Head Screw40 mm
DIN 7991 M20 × 50 Hexagon Socket Countersunk Head Screw50 mm
DIN 7991 M20 × 60 Hexagon Socket Countersunk Head Screw60 mm
DIN 7991 M20 × 80 Hexagon Socket Countersunk Head Screw80 mm
DIN 7991 M20 × 100 Hexagon Socket Countersunk Head Screw100 mm
ISO 10642 M20 × 30 Hexagon Socket Countersunk Head Screw30 mm
ISO 10642 M20 × 35 Hexagon Socket Countersunk Head Screw35 mm
ISO 10642 M20 × 40 Hexagon Socket Countersunk Head Screw40 mm
ISO 10642 M20 × 50 Hexagon Socket Countersunk Head Screw50 mm
ISO 10642 M20 × 60 Hexagon Socket Countersunk Head Screw60 mm
ISO 10642 M20 × 80 Hexagon Socket Countersunk Head Screw80 mm
ISO 10642 M20 × 100 Hexagon Socket Countersunk Head Screw100 mm
DIN 933 M20 × 30 Hexagon Head Screw / Bolt — Full Thread30 mm
DIN 933 M20 × 35 Hexagon Head Screw / Bolt — Full Thread35 mm
DIN 933 M20 × 40 Hexagon Head Screw / Bolt — Full Thread40 mm
DIN 933 M20 × 50 Hexagon Head Screw / Bolt — Full Thread50 mm
DIN 933 M20 × 60 Hexagon Head Screw / Bolt — Full Thread60 mm
DIN 933 M20 × 70 Hexagon Head Screw / Bolt — Full Thread70 mm
DIN 933 M20 × 80 Hexagon Head Screw / Bolt — Full Thread80 mm
DIN 933 M20 × 100 Hexagon Head Screw / Bolt — Full Thread100 mm
DIN 933 M20 × 120 Hexagon Head Screw / Bolt — Full Thread120 mm
ISO 4017 M20 × 30 Hexagon Head Screw — Full Thread, Product Grade A/B30 mm
ISO 4017 M20 × 35 Hexagon Head Screw — Full Thread, Product Grade A/B35 mm
ISO 4017 M20 × 40 Hexagon Head Screw — Full Thread, Product Grade A/B40 mm

Showing the first 40 of 74 specification pages.

Related

Other pitches at the same 20 mm diameter — a fine pitch on a coarse diameter, or the reverse, is the usual substitution question.

M20 × 2 fineM20 × 1.5 fine

Neighbouring sizes in ISO Metric.

M16 × 1.5 fineM18 × 2.5M18 × 2 fineM18 × 1.5 fineM20 × 2 fineM20 × 1.5 fineM22 × 2.5M22 × 2 fine