What I'm looking for has a 2-1/8" round mushroom that only protrudes from the wall's surface about 1/4" total. It looks like the head of a carriage bolt, only much larger in diameter in order to spread the holding power over a larger area. There are pictures of them in the BSP for coin phone installation, but I can't get a picture on here.
Acorn nuts, etc. protrude too far out and there is an issue with appearance once a nut and washer are used. If all else fails, we may just have to go the route of long carriage bolts.
