The Master Lock 110-120V plug lockout surrounds and grips the prongs of an electrical and combines with a padlock (sold separately) to help protect against plug connection during maintenance and repair, and fits two-prong 110-120 volt plugs with and without ground. When plug prongs are inserted into the lockout, its locking mechanism grips the prongs and exposes a locking hole that accommodates padlock shackle diameters up to 1/4" (6 mm). This lockout is made from a red polycarbonate for visibility and impact resistance, and includes three "DANGER" labels, one each in English, Spanish, and French. This device is part of a lockout/tagout (LOTO) safety procedure required at facilities where electrical plugs need to be isolated during maintenance and repair.

Lockout/tagout (LOTO) safety procedures require that lockout devices meet Occupational Safety and Health Administration (OSHA) 1910.147(c)(5) standards for quality assurance. LOTO devices use color, warning labels or tags, and sometimes a physical barrier to help prevent machine operation or power activation during maintenance and repair.

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