The Molex 1731120059 is a jackscrew socket from the FCT line, purpose-built for D-sub backshells. It carries a 4-40 UNC thread and a threaded portion below the head measuring 0.315" (8.00 mm) — the standard length that lets the screw engage the mating receptacle without bottoming out in a typical backshell cavity. This is the hardware that locks the cable-side backshell to the panel-mount D-sub, keeping the assembly tight under vibration and preventing the connector from backing off the mounting flange.
Thread Size and Fit — What 4-40 Means for Your Assembly
It matches the threaded inserts in the mating D-sub receptacle and the clearance holes in most metal or plastic backshells. The 0.315" threaded length below the head is enough to pass through a standard backshell wall and engage the receptacle threads by several full turns, giving a solid mechanical lock. If your backshell has a thicker wall or a recessed insert, check that the 0.315" projection still leaves enough thread engagement — it usually does for standard-density shells.