3G and 4G. Basic Acme dimensions are given in accompanying tables. Centralizing Centralizing Acmes have limited clearance at the major diameter of screw and nut and are used . -TPI-NG-STUB-ACME-EXTERNAL for screw threads or -TPI-NG-STUB-ACME-INTERNAL for nut threads. Where “” is the nominal major diameter given to four . Types: Gift Cards · Stainless Steel · Automotive.