FIP

FIP stands for Female Iron Pipe and refers to the internal NPT threads molded or cut into a fitting or component. Unlike sweat or compression connections, FIP threads accept male NPT pipes and fittings screwed directly in. The thread form is NPT (National Pipe Thread), which is a 60-degree tapered thread that seals under compression as the male fitting tightens.

In the field, FIP connections are common on valve inlets and outlets, iron elbows, tees, and adapters. You'll wrap the male threads with PTFE tape or pipe dope, screw them in hand-tight, then wrench them another one-and-a-quarter to one-and-a-half turns. Over-tightening splits fittings; under-tightening leaks. Iron fittings with FIP threads are durable but brittle—drop one and it will crack.

FIP shows up in supply lines, drain valve connections, and rough-in work where threaded connections are code-approved or preferred. Always confirm the fitting is actually iron or compatible material before torquing hard; some pot-metal or cheap brass adapters will snap if you treat them like real iron.