I find it quite confusing understanding the different fitting sizes, 1/4 BSP, 1/2 BSP and identifying which size is which. I have Googled but I can't really find anything relevant. Perhaps I've missed something I'm looking for clear explanation of sizes and also how to size, measure some fittings I already have, also the American NPT standard. Also a quite comprehensive guide showing various types of nipples, reducers and other air fittings. Cheers.