Ultimate use sx 27.2mm seat post shimthis ultimate use shim system allows you to fit a 27.2mm seat post into virtually any frame size. The shims are made to 100mm length and are longer than other shims on the market, giving your seat post much better support inside the frame.high quality constructionthe machined aluminium shim is machined to very high tolerances from 6082 t6 aluminium and then black anodised to protect from corrosion. The machined plastic shim is used for the larger sized shims and they are machined to very high tolerances from filled engineering thermoplastic upvc. This keeps the weight down, as the shims get thicker.thinnest sizes in aluminiumshims are available in aluminium and thermo plastic, despite the latter being a lighter solution, its material characteristics limit the thickness of the id od measurements. Aluminium is used to achieve the thinnest shims as it is a more robust material.featuresmost of the sizes are made from a resin material for performance reasons thermoplastic upvc, some smaller sizes, will be aluminiumall these shims have internal diameter 27.2mmbuy ultimate use components from chain reaction cycles, the world's largest online bike store.