NPT or National Pipe Thread has become a US standard for tapered threads used on pipe and fittings. The taper rate for all NPT thread is 1/16 th of an inch. When torque is applied to an NPT fitting compression will cause the flanks to create a seal; as opposed to the alternative parallel or straight thread fittings, which thread merely to hold pieces together not to provide a seal.
Acme inlet threads have become the preferred thread configuration in the golf course irrigation market. An Acme thread has a flat apex and valley, and a wider tooth shape than an NPT thread. The wider tooth means it can withstand a greater load than a similarly sized square thread or NPT thread. An Acme thread also contains an O'ring to create a better seal.
Hunter manufactures Acme Adapter Bushings in sizes ranging from 1" to 1 1/2" and multiple configurations are available to convert female and male NPT threads to ACME.
Note: Acme threads are not compatible with NPT or BSP fittings.