LOCK-NUT. Whenever a nut on a bolt or stud or shaft is subjected to vibration it is likely to work loose ; therefore, in the majority of prime movers and power-driven machinery, lock nuts are to be found. These either give a frictional grip suf ficient to withstand jarring loose, or a positive lock. An expensive or delicate type is not admissible, hence the standard devices are limited in number, notwithstand ing that patents for nuts are being taken out constantly. The familiar double nut device gives great friction of one face against the other and of the threads. The helicoid nut is used alone, and is made as a spiral spring, slightly small in the threaded hole. When run down with a wrench or spanner (British term) the coil is slightly sprung apart, and on touching the face of the object becomes powerfully compressed. The Dardelet creates friction between bolt and nut by a taper incorporated in the thread form. The Thackray washer gives friction under the nut, by its com pression. The Grover washer has one coil. For fastenings where
there must be no possible risk, either a split-pin is passed through a hole drilled through nut and bolt, or in the portion of bolt standing above the nut. Or a slotted nut is employed, giving the choice of different distances up and down the bolt, the split-pin passing through the bolt always at one place. The castle nut has the slots cut in a projecting portion above the nut proper. Other devices include a plate with corner turned up to catch against a flat of the nut and prevent rotation, a piece of wire hooked in a hole in the nut and its end caught in a slot in the bolt, or a loop sprung around into a groove in the nut and then into a hole in the bolt. Many large nuts are locked with a lateral screw passed through to press on the bolt, while another way is to partly saw through the nut and tighten the split with a screw, so causing friction of the threads on the bolt.