Please can someone explain how the non-metric bolt strength system works - grade s, grade r etc.
What strength would I need for 3/8" suspension bolts?
Thanks
Dave

Grade S = 8.8, I think

Yep.
Tensile Strength
Grade 'R' 45-50 Tons/Inch²
Grade 'S' 50-55 Tons/Inch²
Grade '8.8' 50-55 Tons/Inch²

from http://www.namrick.co.uk/boltspec.asp

Thanks