This Reese Towpower trailer safety chain with coupler pin is designed for multiple uses, but specifically for trailer coupler levers with a 5/16" diameter hole. Inserting the pin allows the trailer coupler lever to remain in a safely closed position while in use and an open position when uncoupling. The safety chain allows for the pin to hang freely while not in use, which is ideal for marine applications. Easily attaches to coupler with ring. Zinc-plated for durability. 1-1/8" long pin. 7" long chain.