Today we are going to show you a lock from Master Lock, a trailer coupler lock part # 377DAT. We will show you how to operate the lock. You simply turn the key, pull back the shackle, install on the coupler and push the shackle back in. This lock is not limited to the coupler you see here, it will work with all couplers that have this flange around it, and as long as you can insert the ball you will be fine. This is the Master Lock trailer coupler lock, part # 377DAT.