Troy Bilt Tiller Tine Worm Gear part# 1901976 has an outside diameter of 3-1/4" and a 1" inside diameter. This gear has 30 teeth and has a keyway cut into the inner bore. Following are some models that use this gear; 12068, 12069, 12070, 12071, 12074, 12075, 12080, 12081, 12082, 12083, and 12088. There may be models that use this part that we do not have listed, so refer to your owners manual for the correct part number for your tiller.