seatpost sizes

Hey fellows, i’ve just got a new frame, just wondering whats the deal with seat post sizes?
the frame specs say its a 31.4 but i cant seem to find any seat post with this measurement.
does this mean ill just need to use a shim??

The main issue is getting a nice seat post in that size. But they certainly are available:

http://www.wiggle.co.uk/p/cycle/7/Push_Alloy_Seat_Post/5300001914/

or even

http://cgi.ebay.com.au/SELCOF-50-Polished-Alloy-Seatpost-31-4-400mm_W0QQitemZ330355273991QQcmdZViewItemQQptZUK_sportsleisure_cycling_bikeparts_SR?hash=item4ceab57107

I know how you feel - I’ve got an old bike that takes a 26.4mm post… Kind of hard to find other than crappy kalloy ones. Ebay ended up working for me in this case - in fact there’s a fairly cool lookin Selcof and two FSA 31.4 MTB posts on the 'bay right now - search for ‘31.4 seatpost’

cheers dude