The Molex 1731120300 is a threaded block insert from the FEK, FCT 173112 series, designed as a latch block accessory for D-sub backshells. It carries a 4-40 UNC thread — the standard jack-screw size used across the D-subminiature connector family to secure the backshell to the connector body. This isn't a connector itself; it's the threaded insert that gives the backshell its captive screw, letting you tighten down the cable exit without the nut spinning loose inside the assembly.
Thread Size and Physical Fit
The defining spec here is the 4-40 thread — a #4 screw with 40 threads per inch, the same thread used on standard D-sub jackscrews. That means this insert fits any D-sub backshell that accepts a 4-40 threaded block, which covers the vast majority of standard-density D-sub backshells on the market. If you're replacing a lost or stripped insert on an existing assembly, the 4-40 thread confirms it's a drop-in swap without re-tapping the backshell.