The 5555140-2: The integrated shield with an EMI finger provides a low-impedance path to chassis ground, reducing radiated emissions and improving immunity in electrically noisy environments. This is the primary reason to choose this jack over an unshielded version in equipment like routers, switches, or factory-floor controllers where cable-borne noise can couple into the signal pair.
Mechanical Retention and Assembly
The right-angle tab-down orientation means the jack body sits flush against the PCB, with the RJ plug entering parallel to the board — a common layout for rear-panel I/O on a card-edge.
The Cat3 rating indicates it meets the performance requirements for voice and basic data transmission up to 16 MHz — fine for analog phone lines, ISDN, or low-speed Ethernet, but not for 100BASE-TX or higher.