The Sterling Lock Manufacturing Company established in 1919 became part of Engineering Unlimited, Inc. in 1970. The unique zinc-plated, steel rotary shackle padlock is still helping utilities prevent revenue loss and vandalism 90 plus years later. Over the years, Engineering Unlimited added solid brass padlocks, One-Shot seals and disposable aluminum enclosure locks to the Sterling line. As they were in 1919, all Sterling Security Products are made right here in the U.S.A.