Valve clearance was adjustable by screws and locknuts on the rocker arms. Security locknuts are fastened onto a mating bolt to form a bolted joint. In addition, mills use security locknuts to hold mill liners in place. B16.14- Ferrous Pipe Plugs, Bushings, and Locknuts with Pipe Threads. Security locknuts are found in a variety of industrial applications. This entire target assembly was secured at both ends with locknuts.