The OTR 1-5/16" Hex Insulator Box Lock Nut is for use in Mack vehicles Designed to fit securely and efficiently into the 1-5/16" hex insulator box on Mack vehicles. This lock nut is made from high-quality materials to ensure reliable performance and long service life. It meets all the necessary safety standards for Mack vehicles and is designed to fit securely and efficiently. With its durable construction and reliable performance Lock Nut is the perfect choice for any Mack vehicle owner. FleetPride is your First Click in Heavy Duty®.