scope:

INTRODUCTION

The purpose of this Defence Guide is to provide designers and users with advice on the choice and application of screw threads. It is based on investigations by the Mechanical Engineering Research Laboratory (MERL) of the Department of Scientific and Industrial Research (DSIR) into the mechanical strength of bolts and nuts with UNC, B.S.W., UNF and B.S.F. threads.

Because of failures of UNF threads in certain applications where B.S.F. threads had previously been satisfactory, it now appears that the change of pitch/diameter ratio should be accompanied by some adjustment of design practice and refinement of workshop practice to bring out the best qualities of the finer thread. This Defence Guide draws attention to the troubles experienced and suggests how they may be avoided in future.