This is an optional Traxxas TRX-4M Aluminum Steering Link & Servo Horn (Blue).
Eliminate flex and increase the steering precision of your TRX-4M™ with this aluminum steering link. The link is made from high-grade 6061-T6 aluminum for maximum strength and durability and then brightly anodized for a stylish look. Includes metal servo horn, spacers (2), 3x6 mm screw, and 2.5x7 mm screw.