scope:

INTRODUCTION

This Defence Guide has been revised primarily because of the publication of the revised edition of B.S.17687. This no longer shows code symbol 'R' as the recommended general purpose bolt but introduces grade 'S', of a slightly higher tensile strength, in its place. It also reclassifies nuts into three numbered grades and introduces proof loads for both bolts and nuts. This publication of B.S.3580 is also taken into account.

The purpose of this Defence Guide is to provide designers and users with advice on the choice and application of screw thread. Is 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.