1/2” bsp - British Standard Pipe
BSP is a British standard for pipe threads defined by ISO 7 & ISO 228. It is the most commonly used pipe thread system outside the USA. In North America, the more popular standard is NPT.
Although it is a British standard and the nominal pipe sizes are in Inches, the dimensions are defined in millimeters.
Most popular and most range available :
Range within the safety value – 15 pressure per square inch (psi), 18, 20, 22, 25, 30 & 35. Any range is possible to make.