What pipe do the PROTO J140 internal pipe wrenches work on?

The PROTO J140 internal pipe wrenches are made to fit the inside of Schedule 40 pipe only in sizes 3/8, 1/2, 3/4, and 1 inch.
The schedule of a pipe determines the thickness of the walls of the pipe. Outside diameter usually remains constant, so this means the different schedules determine how large or small the inside of the pipe is.