The following website gives some insight into British bolt grades......
An R rated bolt is similar to a Grade 5 according to Curt, the author of the
post on that site.
----- Original Message -----
From: "Bob Danielson" <firstname.lastname@example.org>
To: "Randall" <TR3driver@ca.rr.com>; "'*Triumphs List'"
Sent: Wednesday, November 03, 2010 8:00 AM
Subject: Re: [TR] Bolt Grade
> And I believe that the unthreaded shank is precision ground which is why
> driveshaft and axle bolts cost more ($2 each) then standard bolts. They're
> also harder to find from suppliers other then the usual LBC sources. I
> think Randall told me that many years ago!
> Bob Danielson
> 1975 TR6 CF38503U
> Running w/ Throttle Body Injection,
> Toyota 5 speed & Nissan LSD
> From: "Randall" <TR3driver@ca.rr.com>
> Sent: Wednesday, November 03, 2010 9:18 AM
> To: "'*Triumphs List'" <email@example.com>
> Subject: Re: [TR] Bolt Grade
>>> A friend wants to replace
>>> this bolt with a US equivalent
>> I can't answer your question, Alex, just wanted to point out that there
>> be more to that bolt than just grade. For example, TR driveshaft bolts
>> a particular diameter and length of unthreaded shank, and unusually short
>> IMO it's unlikely to be any stronger than SAE grade 5, but that's just a
>> guess. One way to estimate it is to look at the torque spec. Standard
>> torque for a grade 5 7/16-20 is 75 ft-lb. If the specified torque is
>> than 75, it's probably less than a Grade 5 bolt.
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