Many frames on the market today are manufactured with proprietary or uncommon seat tube IDs. Seatpost options are reduced drastically for these unfortunate frame owners, and finding a lightweight seatpost may be all but impossible. As a solution to this problem, USE manufactures high quality seatpost shims which adapt these frames to the most common seatpost sizes (27.2 and 31.6mm). The smaller shims are machined from aluminum and black anodized to prevent corrosion. To save weight on the thicker shims, high strength black delrin plastic is the material of choice. We highly recommend measuring the inner diameter of your seat tube before ordering to confirm sizing. Frame manufacturers listed have several different seat tube sizes in their product ranges.