British standard pipe is also referred to as BSP. These type of gages are used for joining or sealing pipes. BSP previously was compliant to a standard called BS-2779. This has since been replaced with ISO standards.
British threads fall into two categories, parallel and taper. The parallel type threads maintain a constant diameter along the full length of the thread. This type of thread does not get tighter as you twist it together. The taper type thread changes diameter along the length of the thread, either increasing or decreasing. A taper thread does get tighter as it is twisted together. A BSP when it is joined together has one of two kinds of joints. The first called jointing threads actually creates pressure-tightness by joining the two threads together. In this instance, the male threads are always taper. The international standard (ISO) require the female threads to be parallel. The second type of joining together is long screw threads. This uses parallel threads on both the male and female parts. As a result a tight seal is created with an O-ring and a backnut.
BSP has its own standard which uses thread plug gages and thread ring gages to calibrate them. They check tolerances on the internal and external threads respectively and come in sixteen different sizes; 1/16 to 6 inches. For any questions about which gages is right for your needs, please contact us and one of our engineers or support team members will be happy to assist you.