I splashed out on a new fork from Planet X (and when I say 'splashed out' I mean 'bought the one in the colour they are selling cheap') for a frame I've had sat in the shed for a while. While the frame has been gathering cobwebs I've been picking up other bits for it, so I've been putting it all roughly together this week. Anyway, when I put the front caliper on the fork, which being carbon is quite fat at the crown, I can only tighten the allen-head-nut thing half a turn, which does not feel like anything like enough thread to keep it all together when I have to slam the brakes on. The picture is intended to show the size of the bolt compared to the crown. There is a recess in the fork so the allen-key-nut thing does sit inside the fork, but I can still only get half a turn before it's tight. I have concluded I need a longer allen-key-nut thing, but if I google of that not much useful comes up. Can someone tell me the proper name for the loose bit shown below please?