Plug

A plug is a threaded closure installed into a threaded opening, which distinguishes it from a threaded cap that closes over a mating end. The generic identity does not establish head or tool-interface geometry and must not be assumed square, hexagonal, solid, or cored. Selection should define the actual plug form, its thread size and form and the mating opening, sealing method, tool access, material, and service conditions. Safe isolation, depressurization, and control of trapped fluid are required before removal.