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
(Please note the grey renderings and 3D 'image' show the latest version of the design, the other renderings have not nescessarily been updated. If you have questions please let us know)