Now, if someone can tell me why it's called "1/2" Pipe Thread" when it's much larger than 1/2" - more like 3/4" OD - I'd love to know... Maybe it's actually 1/2" ID pipe?? Lord only knows...
Pipes are like that. It's what keeps plumbers in business. The bigger the pipe, the closer the size name is to the actual outside diameter. A nominal 10" or 12" pipe is about 3/4" "oversize" but a 1/4" pipe has an outside diameter a bit over 1/2". The nominal size is roughly the inside diameter.
Most pipe threads are tapered so they make a better seal. The open end is a little undersize so it starts screwing in easily, then gets tighter as the inside and outside diameters get closer together. The T in NPT stands for "tapered." MPT and FPT, however, add the information that it's a male or a female thread. Copper and plastic pipes live in a different world, though a 10 foot piece of 1/2" plastic pipe, copper pipe, and steel pipe all hold the same volume of water.
See? It's a lead pipe cinch. Now go fix that leaky sink toilet!