This is an optional Traxxas Big Bore Shock Set, and is intended for use with the Traxxas Nitro 4-Tec. Traxxas Big Bore shocks provide ultimate dampening control. They’re hard-anodized, Teflon-coated and have large cylinders for greater oil capacity. Adjustments are a snap with clip-on spring pre-load spacers and installation time is reduced because the shocks are sold pre-assembled.