AMONG many devices for preventing nuts from working loose there is one in common use consisting of a cotter pin which passes through a hole drilled in the bolt. However, this is not perfectly secure. The writer has found the following method better: It consists in slotting the end of the bolt, lengthwise, with a hack saw, and after the nut is screwed into place, driving a small wedge into the hole to spring the ends of the bolt enough to prevent the nut from turning. The wedge itself may be held in place by bending the pointed end slightly. When it is desired to remove the nut, the wedge may be driven out, whereupon the nut may be unscrewed very readily. Sometimes bolts are riveted or center-punched in order to keep the nuts in their place. This, however, makes it difficult to remove the nuts and it requires that they be re-tapped. Furthermore, the bolts themselves must be run through a die before they may be used again.