Stainless steel caps, also known as plugs or end caps, are pipe fittings welded to the end of a pipe or screwed onto the external threads at the pipe end to seal the pipe. They are used to close off pipelines and serve the same function as plugs.

Forged socket-type pipe caps include designs such as domed caps, conical shells, reducers, flat caps, and tapered necks.

Domed caps include: hemispherical caps, elliptical caps, dish-shaped caps, and spherical caps. From a stress perspective, the performance of domed caps deteriorates progressively from hemispherical caps, but in terms of manufacturing difficulty, they become progressively easier to produce.