THREAD HEIGHT (DEPTH)

THREAD HEIGHT (DEPTH)

Thread height: is the distance between the crest and the root of the thread, normal to the axis of the thread. Several issues are easily detected by simply inspecting thread height.

It is designated with hs for external threads and hn for Internal threads. Because in all threads, either the crest or the root must be relieved, the height is a reference dimension and is usually not controlled.


Thread Height Formulas

ISO metric threads consist of a symmetric V-shaped thread. In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. The thread depth is 0.54125 × pitch. The outermost 1⁄8 and the innermost 1⁄4 of the height H of the V-shape are cut off from the profile.


\( \large h_{n} = h_{s} = \frac {\left (Major Diameter\,-\,Minor Diameter\right )}{2} = \frac {\left (d – d_1\right )}{2} \)
\( \large d_1 = d – \frac{5}{8}\times\sqrt{3} \times P \)
\( \large h_{n} = h_{s} = 0.5\,\times\,\left (d – \frac{5}{8}\times\sqrt{3} \times P \right )= 0.54126588 \times P \)

Where:

  • hn – Internal thread hight.
  • D1–Minor diameter of internal thread.
  • D –Major diameter of internal thread.
  • hs– External thread hight.
  • d1– Minor diameter of external thread.
  • d – Major diameter of external thread.

    • Note: From the formula, the thread height depends solely on the pitch. Threads with a fine pitch will be more shallow than larger pitch threads, independent of the diameter.