This is an optional Traxxas Hard Anodized Teflon Coated Big Bore Rear Shock Set. Traxxas Big Bore shocks provide the ultimate in damping control. They’re hard-anodized, Teflon-coated and have large cylinders for greater oil capacity. These shocks also include the super smooth, long wearing titanium nitride (TiN) coated shock shafts. Adjustments are a snap with clip-on spring pre-load spacers and installation time is reduced because the shocks are sold pre-assembled.