Measuring fitting sizes

Nominal pipe size refers to the inner diameter of a pipe. Pipe fitting size refers to the pipe size that the fitting fits to. For example a 1/2″ pipe, the inner diameter of the pipe would be 1/2″. Outer diameter would depends on the wall thickness. To find the correct fitting size, measure the outer diameter of the threads.

• For a male thread, measure the outer diameter  (OD) of the thread.
• For a female thread, measure the top diameter of the opening (OD).

Measure the outer diameter of the thread, then look up the table below for the next nearest nominal pipe size.