FED-STD-H28/21B

Abstract

The metric screw thread standards described herein constitute the basic standards to be used by the Federal Services. This document contains general standards for 60&#176;, symmetrical threads The M profile and the MJ profile. <br>Screw threads covered in this section are only for sizes of 1.6 mm and larger. For smaller sizes, use miniature threads in accordance with FED-STD-H28/5. <br>The M profile is intended for general purpose metric screw thread applications. With the standard tolerance class 6H/6g it is to be used for metric applications where inch class 2A/2B has been used. <br>The MJ profile is to be used for metric applications where inch class 3A/3B and UNJ threads have been used. It is recommended for screw thread applications requiring the most efficient use of material (maximum loads with minimum material), fatigue life and stress levels commensurate with the physical size and weight of the product. <br>NOTE: The MJ profile provides a mandatory-controlled rounded root, for external thread, with an increased minor diameter. The rounded roots greatly reduce the concentration of stress, hence increase the fatigue life of the part. External threads produced by rolling after heat treatment and with rounded roots more than double part fatigue life. Its large core diameter improves the static tensile strength.