The adjustable seat post shim will adapt common seat post sizes to suit more obscure seat tube diameters.
The 25.4mm Shim takes a 25.4mm seatpost and the adjustment ranges from 26.4mm to 28.0mm diameter frames
The 26.4mm Shim takes a 26.4mm seatpost and the adjustment ranges from 28mm to 30mm diameter frames
The 27.2mm Shim takes a 27.2mm seatpost and the adjustment ranges from 29.6mm to 31.8mm diameter frames