This goods is five group of light and handy gears that is engineering plastic material,It's 1.6~2.5 transimission ratio. Very good used for DIY project(like a small mechanical motion device, application in toy and robot) Feature: material:engineering plastic good wear-resistance low niose transmission smooth and steady. Specification： It has 5 group high speed gears,different transmission ratio as follow: 2.5 : 1（32T+13T） 2.2 : 1 (31T+14T) 2.0 : 1 (30T+15T) 1.8 : 1 (29T+16T) 1.6 : 1 (28T+17T) specially: They are pairs using with one to one For any technical support or suggestion, please kindly go to our forum.