This chain guide has adjustable chain line, so you can adjust to the suitable location to acquire perfect chain tension.It is wear-resistant and this chain guide can effectively prevent the chain drop and chain jump.Made of high-quality materials, it is practical and durableThe length of the purple chain tensioner is 9cm, the width is 5cm and the height is 5cm. The length of the black chain tensioner is 11cm, the width is 10cm and the height is 4cm.It is suitable for single-speed vehicles to solve the problem of chain tensioning .Item Name: Bicycle Chain GuideMaterial: Aluminum AlloyApplication Range: 13-23TSize Details: Purple Type Size: 9cm x 5cm x 5cm/3.54" x 1.97" x 1.97" (Approx.)Black Type Size: 11cm x 10cm x 4cm/4.33" x 3.94" x 1.57" (Approx.)Notes:Installation method: shift the chain backward and install it in the frame hook screw hole.Due to the light and screen setting difference, the product's color may be slightly different from the pictures.Please allow slight dimension difference due to different manual measurement.Package Includes:1 x Chain Tensioner