Pls note about the Size: BSP parallel thread size fittings and their specifications can be identified by completing a few calculations. To find the thread size: 1) Measure the O.D (Outer diameter) of the BSP thread. 2) Take the O.D measurement in inches and subtract 1/4 (.25″). For example, a BSP parallel male thread measures out to O.D 1″. Subtracting 1/4 gives a thread size of 3/4 also known as “dash” 12. Once you have the thread size, you then need to determine the number of threads per inch to verify that it is a BSP fitting.