Gear sets offer 40-, 30- and 20-tooth gears with 3/16" bore to accommodate the most popular dowel size, and a 12-tooth gear with a push-ï¬Ât to 2 mm motor shafts. Inserts are provided, allowing the 3/16" bore to reduce to 3 mm. Gears are beveled for 90° meshing. The 40-tooth gear has an additional hole to create an eccentric movement, or to use with a crank handle" Diameter of each gear equals the number of teeth each gears have. 3 Colors - Red, Green, & Blue, 6 ea - 40 Tooth Gears 40mm diameter, 6 ea - 30 Tooth Gears 30mm diameter, 6 ea - 20 Tooth Gears 20mm diameter, 6 ea - 12 Tooth Gears 12mm diameter