This is a complete set of wheels (4 drive wheels) with two matched tracks.   You need 1 of these for the HD2.

The wheels are CNC cut from 1" thick Rubber and sandwiched between 1/2" UHMW.  Each wheel has two sealed ball bearings in them.  Each wheel has a #35 30 tooth chain aluminum chain sprocket mounted to it.  The wheel shafts are 3/4" 6061 Aluminum steped down to 5/8" for the included sealed ball bearings, then steped down again to 1/2" with a flat spot milled onto it for fastening to the tensioners.  See the drawing for details of the wheel assembly.  The wheels come unassembled, you need to bolt them together per the HD2 manual.

The tracks are 4" wide and have CNC machined timing holes on them to match the HD2 wheels.  The tracks have rubber guides screwed into the side for better tracking.  The track is spliced together with a aligator clip.  The inside of the track and the aligator clip are painted with a rubber epoxy.  The nominal center to center distance of the wheels is 28.375".  If you are not using this with the HD2 your design must allow for alignment and tensioning.

This item weighs ~ 31 pounds and is built to order.  Please allow 1-3 weeks for shipment for standard length tracks, 3-5 weeks for custom length tracks.