Mustang® Nylon German Martingale Rein Set. The German Martingale Rein Set teaches flexion and proper head set. Has traditional martingale action, but the longer fork has a snap-on end to pass through bit and attach to 1 of 3 Dees on the rein. Martingale is made from 5/8" black nylon webbing, white nylon rope and nickel plated hardware. Posted.