In general, smaller fasteners have finer threads, so they have a lower thread pitch. ; Thread pitch diameter, major diameter and minor diameter for M profile external threads are given. Basic Pitch Dia. A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by the hyphen sign, -(e.g., M8-1.25). , Horton H.L. it should be 1.27mm 3b #0 - 80 unf .0519 .0542 .0536 .0002 .0002 0°30' #1 - 64 unc .0629 .0655 .0648 .0002 .0002 0°30' #1 - 72 unf .0640 .0665 .0659 .0002 .0002 0°30' #2 - … If your measurement for a metric screw is a diameter of 4 millimeters, a thread pitch of 0.4 millimeters, and a length of 8 millimeters, your measurement would be M4 X 0.4 X 8M. ;