Here are 3 different kinds in ACEM screw thread : Centralizing ACME, Stub ACME, and General Purpose ACME. Centralizing ACME Screw Threads and General Purpose ACME Screw Threads are defined in ANSI B1.5 while Stub ACME Screw Threads are defined in ANSI B1.8. however, the Stub ACME Screw Threads are defined in ANSI B1.8.. but the 3 differences about these ACNE screw thread aren’t list in the same standard that they share some similar characteristics.  There are all three styles about ACME thread ; all be to regards as a bilateral transverse motion screw thread;, and all improve high strength in easy for  machining and assembly, and  all which are used iin feed and adjusting screws..