American Limited Models HO Scale Working Diaphragm kits make adding operating diaphragms to your passenger cars and locomotives fast and fun. They're accurate models of specific prototypes. Easy-to-build kits feature injection-molded plastic parts, in black or gray plastic. Sprung to hold together on curves down to 24" radius, no minimum radius limitation. Will not interfere with operation of most couplers. All working diaphragm kits include complete instructions. Kits are designed to fit specified cars and cab unit locomotives.