The numbers on top generally refer to the material grades, for instance, 8.8 means the bolt has a UTS of 800N/MM^2 with a yield strength of 80% of UTS 10.9 means UTS of 1000N/MM^2 with a yield strength of 90%. The 3 little dashes also indicate the same information but in imperial rather than metric format.

Standard spanner sizes are 6mm = 10mm, 8mm = 13mm, 10mm = 16mm.

Bolts generally speaking do not indicate the size they are on them, but you can usually tell if they are metric or imperial by the markings above.

hope this helps


> I've been working on Vespas and I dug around under 30 years of junk in my garage and come up with a big container of metric nuts and bolts. So far, I have found the ones I needed, but I'm confused by the marking on them. I can't find anything that has much to do with the size and thread of the bolt, and I'm not even sure that I'm reading the grade markings right. For example, I found bolts 6, 8, and 10 millimeter sizes, but nothing on the head mentions these numbers. What does all this stuff mean?
>
> 8 mm bolt, head takes a 12 mm wrench, marked 4 on the head
> 10 mm bolt takes a 14 mm wrench marked 3
> 8 mm bolt takes 13 mm wrench marked Berner 8.8
> 10 mm bolt takes 17 mm wrench marked metric E1
> 10 mm bolt takes 15 mm wrench marked 9.80
> 6 mm bolt takes a 10 mm wrench, marked 7
>
> Then there is stuff like an 8 mm that takes a 13 mm wrench, and has the word "metric" at the top, a picture of an anchor in the middle, and three little dashes at 3, 6, and 9 o'clock. I also found head markings of "10.9," "er 8.8," and "ORV 80."
>
> Unlike some Americans, I am very comfortable with the metric system and use it all the time, so there is a chance I will understand an explanation.
>
> I think it is possible that they came from Italy, Germany, and Japan. Some of the markings may be trade marks. Can anybody explain this mess to me?
> Thanks,
> How"RinkWorks; *the* place for information"ard