A split aluminium shim that fits over a 25. 4 mm (1 inch) steerer tube changing the outer dimension to 28. 6 mm (1-18 inch). Allows the use of a stem designed to fit 1-18 inch steerer tubes where greater choice is available. Black anodised finish with laser etched detail. 1in - 1-18in (25. 4mm - 28. 6mm).