typo in my earlier post - the thinner long studs are 14mm not 11mm.
also in an email from burtons in January this year requesting details of thier long studs they told me that the ones they supply are 17.25mm o ring and measure 108.5mm from the underside of the o ring shoulder to the end of the thicker half (the end that screws into the block). these are 4mm shorter than the longer ones i have and will not bottom in the block as discussed in my earlier post.