What do you do if your front mech clamp is designed for a 34.9mm diameter seat tube, but your frame has a smaller diameter of 28.6 or 31.8mm. 
These simple and neat split shims allow the mech to clamp smaller seat tubes.
Specifications
Material CNC machined Aluminium
Finish Black anodised
Size options 34.9 to 28.6mm, or 34.9 to 31.8mm