Souriau 851 circular connectors were originally conceived to ensure reliable electrical connections in aircraft but their lightweight compact size and general characteristics have contributed to successful adoption in numerous civil and military aviation applications and also in the fields of professional and general electronics (machine tools, automation, measuring equipment).
Orientation and location is ensured by a system of five raised keys on the plugs which couple with corresponding slots on the receptacles. Connectors with different angular positioning of the insulator relative to the shell can be provided to prevent mating of adjacent connectors with the same contact arrangements. The connector shells are manufactured from aluminium alloy. The insulators are moulded from elastomer and are bonded into the shells. Grommets are also made from elastomer and are supplied with appropriate accessories in the solder version, but are integral with the insulator for the crimp version.