Brithish Bolt Head Meaning

This picture is of the 3/4-16 bolts head which fastens the lower carage to the frame of my XJS.
Asking if anyone here knows the equivalent strength of this bolt. Have found source for a grade 5 but not a grade 8. Thanks for your help.

R O is Rubery Owen, the manufacturer. S is the strength but I can’t find a conversion chart that definitively says the modern equivelent is 5 or 8. Maybe you can. It’s in the suspension, it’s gotta be an 8. McMaster Carr, Fastenall, or SNG Barratt for weird stuff, and prepare to pay up!


Better safe than sorry as they say so ordered two each of Grade 8 bolts and grade 8 lock nuts from McMaster Carr today out of Atlanta Georgia. Bolts are $9.55 each and a bag of five fiber lock nuts where $8.16 plus about $13 in freight. Part Numbers are 91257A884 for bolts and 97135A285 for bag of five nuts. Hope this helps some down the line.
Thanks again for all your help.