This Hop-Up Option set is for use with the new BB-01 chassis cars to protect the drivetrain from sudden surges.Item Contents/InformationGear-integrated shaft (20T) x1Slipper screw x1Plate A x1Plate B x1Slipper pads x21050 ball bearing x1Spring seats x2Spring x12.6mm lock nut x1Adjusting spring tension allows change of slip timing and acceleration traction, to give more stable performance.Features precise and durable gear-integrated shaft.Compatible with the BB-01 chassis.