The 'head' sits on a 'ledge', below which should be a metal washer.
The shank is a 'push fit' thru the butt out to the butt socket. (so yes - the shank is also a 'tightish' fit)
Just a thought - you have removed the leather washer / cover from the top of the bolt haven't you ? ( I assume so if you have managed to get a screwdriver into the slot)Information
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