This is an optional Exotek Associated B6/B6D Direct Spur Hub. This spur mount eliminates the slipper clutch, and is a great option for stock class racing. At a mere 3.5 grams, it is lighter for increased acceleration and a cooler running motor, and is compatible with both Exotek and Kimbrough spur gears for increased gear ratio options! Plus, it is easy to switch back to the slipper setup when conditions call for it.NOTE: Not compatible with Avid, Schelle or similar aftermarket top shafts.Compatible Spur Gears: