It carries a 4-40 Socket thread on the mating face and a 4-40 Screw thread on the back end, which means it screws onto the male jackscrew of a D-sub connector and accepts a standard 4-40 screw through the panel or backshell. This is the piece that stops a DB9 or DB25 loom from working loose on a machine-tool controller or a legacy test rack, one contact at a time.
Thread Size and Compatibility — What Fits
The 4-40 thread is the standard across the D-subminiature world — it is the same thread used on the jackscrews of standard-density connectors. A 4-40 Socket on the jackscrew socket means it threads onto the male jackscrew post of a D-sub plug or receptacle.