If you own a frameset that requires a 30.9mm seatpost, but have or want to use a 27.2mm seatpost this is exactly what you need. This shim transforms a 30.9mm ID seatube to use a more common 27.2mm seatpost. These shims are 100% compatible with nearly any manufacturer frame that uses a standard round seat post. One piece CNC machined from Aluminum alloy Black anodized finish to prevent corrosion Length: 90mm: Weight:38g OMNI Racer is small young U.S. company with a passion for cycling and dedicated to bringing cyclists innovative, lightweight, and high quality cycling components to riders that seek the lightest and best quality products. OMNI Racer's products are engineered to optimize the best structural properties of carbon fiber and high strength alloys, creating components at extremely low weights.