text: The thread form follows the British Standard Whitworth standard:
  * Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)
  * One-sixth of this sharp V is truncated at the top and the bottom
  * The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r ≈ 0.1373P
  * The theoretical depth of the thread is therefore 0.6403 times the nominal pitch h ≈ 0.6403P