The popularity of British Pipe Thread conventions, straight or tapered, depends more on application and design. Whether BSP or BSPT they both have been adopted as metric type pipe threads. BSP is a straight thread similar to a fastener thread and does not seal on the thread surface but relies upon some sort of additional sealing element. BSPT is a tapered thread (1:16 or ¾” in. per foot) that goes into a straight or tapered hole and seals on the thread. American NPT thread is tapered so in the United States the BSPT thread is more familiar.