Dom wrote:
Grade 10.9

Ultimate Tensile Strength 10MPa
Carbon Content 0.9%

This is a very strong bolt. If your application calls for a high
tensile bolt then this is a good choice. You could go for a Grade 12,
but this might be overkill. If the nuts are old, you should think
about getting new ones.

HTH Dom.

The 1st figure is 1/10 the tensile strength and 2nd figure is 1/10 the
ratio between the minimum tensile strength and the minimum yield stress
(or proof stress in the higher strength fasteners as this is), also IIRC
the units are in kgf/mm2. So the yield stress is 90 kgf/mm2 and the
tensile strength is 100kgf/mm2. Not sure what the US equivalent is but
a standard socket cap in the UK is a 12.9, button head is 10.9. IIRC the
socket cap screw in the US have equivalent characteristics to 12.9, and
I think you have an equivalanet to 10.9 also.