What Are The Three Basic Types Of Threads?

What Are The Three Basic Types Of Threads? Three are parallel (UN/UNF, BSPP, metric parallel) and three are tapered (NPT/NPTF, BSPT, metric tapered). Three are pipe threads (NPT/NPTF, BSPT, BSPP) and three are not (UN/UNF, metric parallel, metric tapered). Keep in mind that tapered does not necessarily mean it is pipe thread (for example, metric