The hammer unions nut type is American trapezoidal thread ACME. Different pipe diameters correspond to different pitches. There are three types of ACME threads, namely general-purpose ACME thread, centering ACME thread and short-tooth ACME thread. If it is difficult to use general-purpose ACME threads, such as occasions where the internal and external threads often get stuck, centering ACME threads can be used. Low pitch ACME threads are only used in very special applications where space is limited. The button type used on the union nut is general purpose or short-toothed ACME thread.
The American-made general-purpose ACME thread mark consists of thread size code, feature code, tolerance zone code, inspection system code and rotation code.The dimension code of single-line trapezoidal thread is "nominal diameter - number of threads", and the unit of nominal diameter is inches.The dimension code of multi-line trapezoidal thread is "nominal diameter-pitch P-lead L", and the unit of nominal diameter, pitch and lead is inches.The American ACME thread feature code is "ACME"
The tolerance bands for US general purpose ACME threads are 2G , 3G and 4G . The thread feature feature code and tolerance zone are separated by "-".The inspection system codes are ( 21 ), ( 22 ) and ( 23 ).
Left-hand threads should be marked with "LH" code after the tolerance zone code. Right-hand threads are not marked with a rotation code.

When the union male sub and the nut are connected to the female joint end of the chiksan swivel joints, the high pressure chiksan pup or the integral fittings, attention should be paid to the adaptability of the ACME thread.