This is a set of twelve RPM 4-40 Heavy Duty Rod Ends. These rod ends have oversized hexes and the ball cups are molded from RPM's blend of tough, bulletproof nylons to the strictest of tolerances. If youâre tired of popping ball cups and breaking rod ends, RPM rod ends are the solution! RPM rod ends fit all Associated, Losi, & HPI ball-studs. Like all RPM products, these rod ends are guaranteed by RPM not to break!