SSD RC Traxxas TRX-4M Brass Knuckles. Constructed for high quality heavy brass we have to expect from SSD, these optional brass knuckles are intended for the Traxxas TRX-4M 1/18 micro crawler to add 26g of total unsprung weight to lower the center of gravity, increase the front weight bias and the durability of your TRX-4M front axle.