This British Standard relates to the Heavy Series of Unified black hexagon bolts, screws and nuts having Unified screw threads in a range of nominal sizes from 1/2in. to 2 in. inclusive.NOTE. It is considered that the range of nominal sizes included in this standard is adequate for most of the applications for which this series is likely to be employed, but for the convenience of users requiring larger sizes, the formulae from which the proportions for bolt heads and nuts are derived are given in Appendix A.The steel used for the manufacture of bolts, screws and nuts shall be such that the products possess mechanical properties as follows:Minimum tensile strength Minimum elongation 26 tonf/in2 17%*or 28 tonf/in2 15%In each case the minimum elongation is based on a gauge length of 5.65 .In the case of hot forged bolts made to either of the above mechanical property groups the steel used shall not contain more than 0.06 percent each of sulphur and phosphorus.The choice of material to provide either of the mechanical property groups referred to above will normally be at the option of the manufacturer, except where the purchaser specifically states which of the two he requires. Where the bolts, screws or nuts are required with mechanical properties different from those above the purchaser should specify the properties required in the enquiry or order.

Obsolescent