Locking plugs have curved blades. Mating locking receptacles/connectors have slots to receive the curved blades.  To make the connection the receptacle/connector is fully inserted into plug blades. Then the plug is twisted clockwise, locking the blades. To unlock the blades and remove the plug, twist the device counter-clockwise. Locking blade devices can prevent inadvertent disconnection. Use locking blade devices with critical equipment or in heavily trafficked areas where inadvertent disconnection could pose safety/work stoppage issues.