The SMP-PF-P-HH-ST-EM3: The full detent feature gives it a positive snap-on lock — you feel it seat, and it stays put under vibration. This is the member of the SMP-PF family meant for board-edge mounting through a cutout, with surface-mount shield tabs that solder directly to the PCB ground plane.
This connector mounts to a board edge via a cutout, with the shield termination soldered to the PCB. The surface-mount shield tabs ground the shell directly to the board — no separate ground wire needed. The full detent means the mating half snaps in and stays until you pull it free; there is no secondary lock ring to fiddle with.
The full detent is the mechanical lock that keeps the plug mated when the cable gets tugged or the equipment vibrates. Without it, a standard SMP push-on can pop loose in a high-shock environment. The gold-on-brass contacts and body resist corrosion, which matters when this connector lives in an outdoor cabinet or an engine bay where moisture finds every unsealed joint.