Cannondale CAAD 7 Brake fititng?

shaw8670

I am just building up a Cannondale R700 CAAD 7 frame. The Allen brake nut does not appear to recess, so it doesn't reach the bolt. By my calculation a 30mm long nut would do it, but it doesn't look right? There is a sleeve in the fork crown that looks like it's meant to be there and goes about 3/4 of the way through the crown and the nut fits into it perfectly but the end protrudes, but I can't work out why, unless this is just a cannondale feature? Is this the way these Cannondale Slice forks were made?