Tr18 × 4 Thread Dimensions

Basic information

Designation

Tr 18 × 4

Thread system

Trapezoidal

Series

trapezoidal

Standard

ISO 2901

Basic profile

Trapezoidal basic profile

Flank angle

30°

Dimensions

Major diameter

18 mm

Pitch

4 mm

Threads per inch

6.35

Pitch diameter

16 mm

Minor diameter (external)

15.5 mm

Minor diameter (internal)

14 mm

Thread depth

2.25 mm

Recommended tap drill

Ø 14 mm

These figures follow the Trapezoidal basic profile of ISO 2901. 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 Tr18 × 4. Power threads are not fastener threads — they are found on lead screws, jacks and vice screws, so no bolt or nut in this catalogue is made in this form. The geometry above is what a machinist needs to cut it.

Neighbouring sizes in Trapezoidal.