This is a New In The Box Proven Industries Model 2178-D1 Trailer Lock it is designed to fit Demco Cast raised trigger latch couplers (as seen in the FINE PRINT section). This model was manufactured with a formed carbon steel outer housing to completely encapsulate the coupler head and latch. This lock model will be able to secure most safety chains up to 3/8" in the dedicated chain locking compartment. Designing the best coupler locks is not an easy task. We pride ourselves on producing a "glove like" fit coupler lock. Rest assured that Proven Industries trailer lock products will leave you with simply the best coupler lock on the market. In addition, no other trailer coupler locks can secure your safety chains.