seat post sizing shims use a very common 25.4 inner diameter seat post and outside diameters of all seat tubes in 0.2mm increments
your LBS will measure your frame and order the sizing shim that is appropriate..
next jump is a 27.2 seat post and sizing shims upward from there ..
I have 2 CC 'Thudbuster' seatposts in oversize seat tubes using sizing shims to fit them.
NB: a thicker tube wall will have a smaller ID, a 28.6/1.125" seat tube will be thinner tube wall on top , to accept a 27.2 seat post .
0.7mm to be specific .
Last edited by fietsbob; 11-15-15 at 10:34 AM.