HG 19MM TAPERED ALUMINUM BALL-RACE ROLLERS (RINGLESS/PURPLE)
From the manufacturer:
These tapered rollers give your car a better chance of making its way back onto the track if it happens to climb up the course wall. These 19mm components are crafted in purple anodized aluminum and feature built in 520 ball bearings for super smooth rotation.
2x8mm screws and roller spacers are included.