HPI Racing 2 degree pivot block is constructed of purple aluminum. This is for the Pro4. These pivot blocks allow you to adjust the front and rear of the car in 1/2 degree increments, which helps optimize the suspension on the racetrack for faster lap times. Each block is precision machined from billet aluminum, purple anodized and laser etched for easy identification. These can be used on either the front or rear of your HPI Pro 4 for a wide range of adjustments.