This is a shaft and wheel set for our Mini ATR kits.  The kit includes our 4" tire set and adds a custom hex shaft that is drilled to 6mm on one end and has a 1/4-20 set screw, the other end is taped to a 1/4-20 thread to accept the included machine screw.  The set screw clamps onto the 6mm motor shaft.  This set includes 2 of everything since the tires are a matched set with directional tread.