We were building a bunch of Prusa i3 Rework RepRaps in the DCRL at UWM and we decided to use 5/16" hobbed bolts instead of 8mm hobbed bolts, which meant the gear was the wrong size for the hex head of the bolt. I did a quick search for an Imperial version and didn't find one, so I edited the 8mm gear to be a 5/16" gear.