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 1.6 mm. 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 2.5 cm to 3.8 cm 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.