Pipe over two miles long must also have these words painted in the middle so the fitter will not have to walk the full length of the pipe to determine if it's long pipe. All pipe closures are to be open at one end. All pipe fittings are to be made of the same stuff as the pipe. No fittings are to be put on pipe unless specified. If you do so, straight pipe will become crooked pipe.
Fittings come in all sorts of sizes and shapes.
Be sure to specify the direction you are going when ordering. Flanges must have holes for bolts separated from the big hole in the middle. If flanges are to be blank or blind, the big hole in the middle must be filled in with metal.