Originally Posted by
Chris_W
You'll have to use a bolt with an extremely small, thin head. I recently tried to add one to a large chainring that had a hole drilled for it. It took me a while to find something small enough and for which I could find a matching nut. If the head is too big, the chain can catch on it when in the middle ring.
A couple of minutes with a flat file will thin out the head of any bolt but you make a good point to minimize the protrusion of the bolt head into the gap between the chainrings.