Took a look at some carriage bolts online and most seem to have round tops. Did find some that are flat-top but they don't have the countersink which I put in there to get the tops of the bolts flush. On top of that... I would have to find metric ones because the countersink I cut is 90 degrees but most US countersunk bolts are 82 degrees. Probably would have to hunt around online for ones that would do the trick.