CURT 25035 Trailer Coupler Pin with 12-Inch Chain, 5/16-Inch Diameter x 3-Inch Long. Coupler safety pins simple function of keeping your coupler latch secure. They are constructed from quality materials and have a universal design that allows them be used for a variety of purposes in your towing setup. Made from solid steel to provide more than enough strength to keep your trailer coupler latched down tight. The zinc plating that we use to finish our safety pins offers excellent protection against rust and corrosion. This is necessary for any trailer because of its frequent exposure to the elements. The user-friendly design allows them to be easily handled while maintaining effective security. This safety pin has a pin diameter of 5/16" and includes a 12" chain attachment to mount onto your trailer coupler and prevent the safety pin from being misplaced. Use safety pins for securing trailer couplers, jacks, caster wheels and more.