The TE Connectivity 501933-4 is a duplex multimode fibre optic adapter that converts from an FSD receptacle to an ST receptacle. It is a panel-mount flange design, housed in a beige plastic body, and includes a dust cap. The S-keying ensures correct polarity alignment in duplex systems, preventing a flipped pair from being inserted the wrong way. This is the part to specify when a patch panel or bulkhead needs to transition between FSD-terminated patch cords and ST-terminated equipment ports.
Installation and Polarity Check
The flange mounting requires a rectangular panel cutout matching the adapter body dimensions — the flange sits flush against the panel face and is secured with hardware (not included). The S-keyed alignment slot forces the duplex pair to mate in the correct orientation, so the transmit and receive fibres land on the right ports. The included dust cap protects the internal alignment sleeve when the adapter is unmated; leave it on during shipment or storage to keep the ferrule bores clean.