Originally Posted by
Bush65
The earlier rover diff had SAE Grade 5, 3/8" UNF bolts. Their strength (SAE Grade 5) is comparable to ISO Property Class 8.8.
With UNF bolts, SAE Grade 8 is readily available. I don't have my bolt hanbooks and Standards with me, so I can't confirm if Grade 8 is comparable to Class 10.9 or 12.9 and I don't want to go from memory.
However I do know that Grade 8 is the highest strength in any of the Standards for imperial bolts. Now Unbrako socket head cap screws are Class 12.9 and readily available, but the strongest bolts in the world (sorry can't remember the manufacturer, but I have a catalogue - not with me) as a stock line are called Grade 9 - these have the strength of Grade 9 if the Standards were to be extended to include such a high strength - so this make me think that Grade 8 is stronger than Class 10.9, but may be a bit less than Class 12.9