The CF3 Pro Carbon seat post is rated for road and dirt-road use only. No MTB. No CX. The only size available is 27.2 x 330. Seat tube shims are not allowed to be used with the CF3 Pro Carbon. Your bicycle seat tube must be 27.2. The seatpost comes stock out of the box with the ability to fit round saddle rails (7x7). The use of oval carbon rails (7x9) requires the separate purchase of the 7x9 Flip Head. Rider and clothing combined weight limit for the CF3 Pro carbon is 220 lbs. There is no crash replacement policy for the CF3 Pro Carbon. Scratched, crashed, dinged, etc are not covered under our 2 year warranty. CF3 Pro Carbon seat posts are not available in the US.