Zenex Thermoplastic Is the Optimal Safety Lock Designed Exclusively for Lockout/Tagout and Meets OSHA LOTO 5 Requirements: Durable; Standardized; Substantial; Identifiable for OSHA Safety Compliance; Stands up to Chemicals, Temperature Extremes & UV Stable. Our Zenex Thermoplastic Locks Include the No. S31, No. S32, No. S33, No. 406, No. 410 & No. 411 Zenex Safety Locks.