Belt adjustment on original VirZoom bike

[Virtual_Davey]

I received the belt that you recommended today, and I do believe it's the correct belt. But when I put it on, it was very loose and needed to be adjusted. There are 2 unusual shaped nuts and bolts, one on each side of the bike, which is used to move one of the wheels, thus tightening the belt in the process. Unfortunately, both of my nut/bolt sets are stripped and I'm unable to tighten anything. I've posted a picture below of the bolts. I need to find replacements but have no idea what these are called. I can find the nuts at Home Depot I'm sure, but the bolts I can't seem to find. I would actually prefer longer bolts, if such exist.
Does anyone know what these are called?