A short guide to metric nuts and bolts （一个简短的指南标准螺母和螺栓）.pdf

A Short Guide To Metric Nuts and Bolts Answers to the most Frequently Asked Questions Standard and Fine Pitch h reads How to identify nut and bolt strength grades How nut and bolt strength grades compare Maximum Tightening Torques Why specii ed torque is sometimes lower than the maximum Spanner Sizes Versus Bolt / Nut thread size Allen Key size versus Bolt / Nut thread size Correct Drill size for Tapping Metric threads in holes Copyright: h omson Engineering Design Ltd all rights reserved Document Number: TESG1 Issue: 1 Date: December 2012 Introduction: Metric Nuts and Bolts This short guide is intended to give a very basic introduc on to ISO metric nuts and bolts. It is intended for those working in plant and machinery maintenance to give enough informa on to ensure that correct replacement parts are idenfi ed and used. Few parts are as cri cal in the assembly of modern machinery as the nuts and bolts which hold it all together and, at fi rst sight, it seems that all metric bolts are basically the same. In fact, of course, nothing could be further from the truth. There are no fewer than 5 diff erent threads for diff erent applica ons and 10 diff erent standard strength grades defi ned for each size of bolt. There are nineteen standard sizes - known as the ‘preferred ‘ sizes and ten less commonly used (the so- called ‘non-preferred’) sizes. The situa on is almost as complex with metric nuts which come in a wide variety of types (full, thin, nyloc, castellated) and 5 strength grades as well as the same range of sizes. The diff erence in strength between diff erent grades is quite drama c: the highest standard grade being capable of carrying more