Tamiya HG Aluminum Ball-Race Rollers. These optional rollers come with 520 bearings preinstalled to allow a super smooth movement. A smooth flat edge is used rather than an O-ring for less friction. The lower friction can allow for increased speed through corners. These rollers may be used in either the front or rear location. Package includes two rollers two spacers and two screws intended for all Tamiya Mini 4WD and Mini 4WD Pro chassis.