MK4 connectors are available in aluminium shells with fine thread coupling and brass shells with coarse thread quick release coupling. They were originally manufactured in accordance with DEF STAN 5321 and afterwards to BS9000 approvals. They are rugged and when used with a range of screened or un-screened outlets, environmentally sealed. They are designed for DC and low frequency applications and have a standard operating temperature of -40 degrees C to +85 degrees C.