From Amphenol, this chassis connector dust cap is part of the Black Zinc connector 62GB series.

Amphenol BLZC (Black Zinc)

Black zinc cobalt plated bayonet locking connectors that are interconnectable and interchangeable with connectors that conform to MIL-C-26482 and BS9522 F0017 requirements. Of a commercial grade they are machined from aluminium alloy and provide durability and resilience in industrial environments. The black plating offers an aesthetically pleasing finish to the connectors. Connector pins and sockets are prefitted solder bucket type.,The cable plugs are supplied complete with backshell.These connectors will also take the spin coupling backshells (stock no. 241-1294 - typically) and have the same thread as 62GB connectors.