Features: brand new and high quality Material: 7075 aluminum alloy high strength metal palin Size: 11t diameter about 41mm, 13t diameter about 49mm Specification: guide wheel with 4/5/6mm axle 7075 aluminum alloy material, one price. Supports most dials on the market, supports 7/8/9/10 speed! Contact us if you have questions,we will try our best to serve for you. Specifications: Color:Black/Blue/Gold/Purple/Red/Silver Size：A:4.15CM/1.63in B:5CM/1.97in C:6CM/2.36in Package Includes: 1 x Wheel Rear Derailleur Pulley. note: For 11t and 13t purchase, 13t is generally considered for long tail rear dial, otherwise 11t guide wheels are used. Please allow 0-1cm error due to manual measurement. Make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you! Selection Principles: 1: Use the same size as the original guide wheel as much as possible and there is no difference. You can choose smaller than the original guide wheel and cannot use the big ones. 2: the guide wheel and the tension wheel are not distinct. Some original rear idler wheels and tension pulley are not the same size and can be replaced. It is necessary to readjust the length of the chain.