13B Railway Train Car Coupler and Draft Gear Assembly The 13B coupler was developed on the base of the 13A coupler and has been widely used in Chinese railway heavy load freight cars since 2007. It is made of E grade low alloy cast steel, with a coupler body minimum failure load of 4005 kN and a coupler knuckle minimum failure load of 3430 kN. The coupling clearance is 11.5 mm, which significantly improves the longitudinal dynamic performance of the train. 13B couplers are