The Master Lock rotating gate valve lockout is a lockable thermoplastic shell that surrounds and covers a gate valve handle and aligns two flanges to form a hasp with up to four holes for padlocks (sold separately) to help protect against accidental valve opening as part of a lockout-tagout (LO/TO) safety procedure required at facilities where the flow of a fluid is controlled by a gate valve. This lockout consists of two halves; one slightly smaller half fits inside the larger half when not in use, for installation in confined spaces and a compact storage footprint. To deploy, the lockout is placed over a gate valve handle, with a center hole fitting over the gate valve stem, then the inner half is rotated out to surround the rest of the gate valve handle. Where the two halves meet, flanges from each half align to form a hasp with up to four locking holes. A padlock shackle placed through any of these holes obstructs the inward rotation action of the lockout, thereby prohibiting access to the gate valve handle. Multiple locking holes provide the ability to require multiple authorizations to allow operation of a locked out gate valve during maintenance or repair. This lockout is made from red Zenex thermoplastic, which is nonconductive and functions in extreme temperatures: -50 to 350 degrees F (-46 to 177 degrees C). On the outer (or top, depending on the orientation of the gate valve,) part of the shell a small circular area can be removed to allow installation over rising stem gate valves. This product includes three (English, French, and Spanish) high-visibility warning labels with erasable areas for task-specific details. One label fits on the lockout at a time. When used according to manufacturer's recommendations, this product is covered by a limited lifetime warranty against defects in workmanship or materials.

Lockout-tagout (LO/TO) safety procedures, as defined by Occupational Safety and Health Administration (OSHA), require that lockout devices be durable and standardized. Lockout devices use color, warning labels or tags, and a physical barrier to temporarily prohibit machine operation or power activation, and help reduce accidents, during maintenance or repair. Gate valve lockouts are lockout devices that temporarily prohibit operation of gate valves by covering the handle with a lockable shell. They are often used to secure fluids in the off position during maintenance or repair when multiple workers are on the job.

Master Lock manufactures padlocks, combination locks, and related security products. The company, founded in 1921, is headquartered in Milwaukee, WI.