"The GK Series Dual Entry Key Operated Safety Interlock Switch is designed for use on machinery where key removal brings the machine to an immediate safe condition. It provides enhanced operator safety when added to hinged or sliding guard doors, screens and protective covers on enclosures. Key sold separately.","A safety lockout device (GKZL2) is available for use with the GKR\/GKL Series. The lockout device is designed to prevent a key from being inserted either manually or by the protective guard being closed while maintenance personnel are working on the machine. When inserted, the lockout device may accommodate up to four padlocks to prevent unauthorized removal of the device. UL, CE, CSA, SIL 3 capable."