Just the thread I was looking for, so I'll jump in with a question until the OP returns. Recently, I discovered that I was missing some 8mm coarse bolts that attach the floor pan to the tractor. Went to the hardware store - they had them, but the original bolts took a 12mm socket, while the replacement bolts needed 13mm.
Yesterday, I had to remove a front tire that went flat. Original tire nuts were 17mm - one was so beat up I had to remove it with vise grips and completely destroyed it. Got replacement 12mm fine thread grade 10 at hardware store and again, it will need a larger socket to tighten.
Eventually, I'll get OEM bolts to simplify servicing, but wondering about the difference in hex bolt head size.