NPT stands for National Pipe Taper, and is the most common U.S. standard for pipe fittings. NPT fittings are measured on the internal diameter of the fitting.

AN fittings were designed originally for the U.S. Military (The "A" standing for Army, and the "N" standing for Navy). AN fitting numbers refer to the outside diameter of fittings in 1/16 inch increments, thus an AN 4 fitting would have an external diameter of approximately 4/16", or 1/4", and an AN 6 fitting would have an external diameter of approximately 6/16" or 3/8". The approximately is important, since the AN external diameter is not a direct fit with an equivalent NPT thread, and the table below, should provide some guidance.

Dash or - fittings are interchangeable names for AN fittings, thus a Dash 8 fitting would be the same as an AN 8 fitting.

BSP stands for British Standard Pipe and is the U.K. standard for pipe fittings.

NPT Size Nearest AN Size Nearest Dash (-) Size

1/8" = 4

1/4" = 6

3/8" = 8

1/2" =10

3/4" =12

1"   =16

1 1/4" =20

1 1/2" =24