Effect of Taper on Screw-Thread Load Distribution

The load distribution on the threads of bolts and nuts, made in the conventional constant-pitch manner and with tapered threads, was determined experimentally and theoretically. The results indicate that substantial improvement, in the order of 2 to 1, in thread load distribution can be made by tapering the thread of either the bolt or nut properly. Material improvement in bolting strength is obtained in applications that normally are conducive to little plastic flow and thus liable to result in brittle fractures, such as are encountered with dynamic loads or static loads at elevated temperatures. Ten years of operational experience on high-temperature high-pressure turbine bolting is cited to substantiate indicated improvements.