This is a pack of two 5x11x4mm rubber sealed "Speed" bearings. ProTek R/C "Speed" bearings are high quality steel/chrome bearings designed for the R/C racing enthusiast.
These 5x11x4mm rubber sealed bearings are the standard bearing for many monster truck clutches, such as the Traxxas T-Maxx and Traxxas Revo. Some racers prefer the rubber sealed bearings for better protection against dirt for their clutch. Please check the manual that came with your vehicle for the correct size if you are not certain.
