Mike,
On the BWD instrument these connectors are recessed deep in an insulator where the rotating part of the mating BNC connector is nestled down inside the same insulator. This prevents any ability to rotate it in the normal locking sense because you can't get to it. The recess obviously keeps all metal portions of the connector away from grabbing probably due to the high voltage rating of this instrument and related safety factors.
Since the BWD instrument inputs are purely differential and each channel has two inputs the shields of the probe cables are at ground level for their normal noise shielding purpose. Since this instrument is designed for connection to the AC mains for analysis purposes the inputs are rated to 1000V. Even with the BNC shells at ground BWD still apparently designed in the extra level of protection by recessing the connectors.
Greg
