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aha! this is what a blaze brake looks like

so to remove the brake just untighten the allen key at the back of the fork. then pull the brake and the pin away from the fork as one unit. the recessed allen key nut is left in the frame and can be removed freely or with some WD40 to loosen it.
this is what the recessed nut should look like, it will be buried in the frame.
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i think there are weird shims which go between the fork crown and frame. They may work depending on the amount of steerer on your fork and the rake/head angle of your frame and fork. Even if they do work they will alter the bikes geometry and can be a bad idea for handling etc.
This is probably why BMX and trick specific frames were designed.
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Finished doing the vivalo pantographing, need to sort out a chain and some wrap+plugs for the bars
Has a fair bit of dura ace but is by no means an NJS build prepares to get flamed

Couldn't get the image to embed with rotation correct but you get the gist of it!
I'd avoid that stem, doesn't match, possibly too long and welded stems like that are more prone to failure* than a traditional stem made from one piece of alloy.
*learned the hard way.
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It's hard to see what part your talking about with this pic. Any chance of a close up.
I dont think I have ever come across a fork crown with a thread for the caliper, normally the bolts holding on the front brake just run through the fork crown and tighten with a nut on the back. In more modern designs this nut is recessed into the fork crown and is tightened with an allen key. It should slide out of the back of the fork crown with a bit of push/shove.

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What are you going to put the nail/screw into? That's probably more important. Any decent screw will hold 7kg as long as it's in a decent piece of timber etc. However if in doubt this wont break the bank £1.31p:
http://www.winstanleysbikes.co.uk/product/17558/Park_Tools_Wood_Thread_Storage_Hook -
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so you can prove that your holiday was bigger/longer/better/more epic :-)
...and then plot graphs about it.