This is a plastic .3 modulus worm gear that fits .8mm motor shafts. Outer diameter is 3.45mm. The total length is 5mm. This is the same gear that is sold with the 70 Tonner finishing kit. No other The Z Maker chassis sold at Shapeways is designed to fit this gear. However, you may find a use for this gear on a modified chassis or a new creation of your own. Happy modeling!