NPT (National Pipe Thread) is a US standard for tapered thread used for fittings, pipes and components. Suffix F for female; M for male. The sealing of the assembly is obtained with PTFE (Teflon®) tape between the threads. For specialty gases installations the most common size is 1/4". Do not mix these fittings with BSPT (British Standard Pipe Tapered Thread) or BSPP (British Standard Pipe Parallel Thread).