This set is designed as an update for Hotchkiss tanks from Bronco (1:35), but may also be used with kits from Trumpeter or Heller. Included are parts for new bogies, idlers, sprockets and return rollers. Additionally a spare road-wheel is included. Finally a jig has been added to help position the bogies correctly. Depending on the kit, different bogies are already in the right position. Those should be used as a starting point for the jig. Assembly instructions can be found here: http://www.shapeways.com/forum/index.php?t=msg&th=10945