[Spridgets] bumper bolt size?

[ryan.kubanoff at comcast.net]

What is the correct size for the front bumber bolt that attaches to the tow loops on a 73/74 midget?  I pulled my bumper off and now it seems either those bolts are really right or i somehow misplace the correct ones.  The other  2 bolts per side went in fine but these particular ones don't seem to fit.  I thought they are 5/16 fine thread but now I am not sure.
ryan