[terry and jo]

I think the markings on the head of the bolt indicate what grade they are. Back in the '80's, I managed a country grain elevator, and they built a new 150,000 bushel grain bin. After we got the thing full, it collapsed. Come to find out, the manufacturer of the bin sent grade 5 bolts instead of grade 8.

Since it has been that long, my memory is a little "loose," but I think the grade 5 bolts had three marks on the head and the grade 8 bolts had 5 marks on the head. Why I'm "loose" on that memory is that it looks like the bolts in Cummin's picture have six marks.

When looking at bolts in the hardware store, you might check the "marks" to see if I'm even close to right. I just went out to look at our Trail-Air pin box and it has six bolts with just 3 marks on the head.

Terry