"AN" THREAD SIZES

"AN"(Army-Navy)sizes were established by the aerospace industry years ago and were designated O.D. of the rigid metal tube that each size fitting is used with. (The chart to the right will clarify this point).

The numbers assigned equate to the outside diameter (O.D.) of the tubing in 1/16". Since tubing and hoses are to be found with assorted wall thicknesses, we can now understand that the designated size number does not necessarily tell you how large the inside diameter will be. (For example, the inside diameter of an Earl's size 6 hose end is nearly as large as the inside diameter of some other manufacturers' -8 hose ends).

Each AN size number has its own standard thread size which can be seen in column three of the chart. Again, these are the same thread sizes that have been used in aircraft and industrial applications for many years.

"NPT" THREAD SIZES

We can now leave AN thread sizing and head on to the next category which is N.P.T. (National Pipe Threads). National Pipe Threads are the next most popular thread size used in "Competition Plumbing". We can actually find a resemblance between the size call outs and the I.D. (inside diameter) of the fitting. The outside silhouettes shown here will help verify your fitting selection.