Threaded Pipe and Fittings

Threaded Pipe and Fittings

Threaded pipe is an all metal pipe (galvanized or brass) used to connect water lines to fixtures and appliances. Fittings for both materials come in a multitude of angles, as well in short straight sections called nipples.

Fittings have threads on the inside (female threads) and nipples and full length pipe have threads on the outside (male threads). Connecting a fitting to a pipe is accomplished by screwing the threads together. Use pipe wrenches to tighten the connection, one wrench holding the pipe and the other turning the fitting or in reverse.

Threaded pipe tips:

Never use a nipple or fitting with rusted threads. Clean the rust off first or the rust will keep the threads from seating properly, causing the joint to leak.

The bigger the wrench, the easier it will be to tighten the fitting.

Avoid screwing a metal pipe deep into a plastic bushing or fitting. Plastic cracks easily.

Always install Teflon tape in a clockwise direction as the threads face you.

Use these fittings to connect pipe together or to change the direction of a pipe, T, elbow or 90, street elbow or 90, plug, cap, coupling, street 45, 45 or union.

Use these fittings to change from one pipe size to another, 1 in x ½ in reducing coupling, ¾ in x ½ in coupling, reducing T and reducing bushings.


When tightening and loosening threaded pipe, you will often need help and that comes in the form of a pipe vise or a chain vise. These are invaluable when you need them.

A chain vise is lightweight and will have to be bolted onto something. A pipe vise is heavy and can often be used without being fastened down. Most spin 360 degrees and will tilt in any direction.

Splicing Galvanized Pipe

Always work with threaded ends when splicing galvanized pipe, even though a fitting called a dresser or compression coupling (a metal fitting with rubber gaskets at both ends) is made to do just that. Avoid these fittings because they tend to blow off the pipe no matter how much you tighten down the end caps.


Lubricating the threads

To keep pipe threads from rusting and seizing once assembled, coat the male threads with a thread lubricant pipe dope or Teflon tape. These coatings reduce friction, allow deeper seating of the pipe in the fitting, prevent leaks, and let you unscrew the joint more easily, if needed. Each has its advantages and disadvantages.

Although all you have to do with a paste is brush it into the threads, its messy ro bring a rag and wipe off any excess. Teflon tape must be wound in a clockwise direction (as you face the pipe end) and even when wound correctly, it can tend to pull itself into a useless string. Winding the tape in a counterclockwise direction will cause it to unwind off the threads as you install the fitting.

Installing a Threaded Fitting

Don’t even think about threading fittings on a pipe unless both male and female threads are clean. Clean heavy rust on male threads by hand, using a wire brush. Alternately, use a bench mounted grinder. If the pipe is in a fixed location, use a wood handled wire brush or mount a circular brush on a drill. Apply thread lubricant to the male threads before screwing the fitting onto the pipe.

Set the fitting against the threads square to the pipe. Turn the fitting clockwise until the threads engage. Keep turning the fitting until it is hand tight.

To get the fitting watertight you must use two pipe wrenches and muscle power. Use one pipe wrench to turn the fitting clockwise and a second wrench on the pipe, applying equal power in opposite directions.

The jaws should face each other. Tighten the fitting until its orientation stops and is lined up with the pipe on the other end. If you go too far, don’t back the fitting off, continue tightening until the faces of the fitting and the pipe meet.

Return to How To Plumb

Return to Home Page

Hard copy and E book for sale. Introduction to Building Mechanical Systems. Click here.

Hard copy and E book for sale. What's Killing You and What You Can Do About It. A humourous look at ageing and disease. Click here.