British Strength Rating Codes

[Healey]

Hi All,

There was recently a question on the Healey list about the strength codes on British fasteners. I've copied the question and my response below and would like any feedback or corrections from this list.

Once again this is for a series of articles for a marque specific British car magazine on British fasteners

Thanks,

Curt
Carlsbad, CA
'55 BN1, '60 AN5 :{) '72 RWA Midget, '06 Cooper S

"Is there a guide somewhere that tells me what the codes mean on British made bolts?

Specifically,

Is type "R" similar to Grade 5 (US) and is Type "S" similar to Grade 8 (US)?

Is R good enough for most purposes on a Healey? Anything that requires Type S?"

To which I answered:

Here is what I have to date with regard to British strength rating codes and their letter ratings.

A - 28 TONS TENSILE, I've never seen a bolt with this rating in 35 years of working on British cars.

B - UNKNOWN, However the 3/8" Bolts that hold the bumper brackets to the frame on my BN1 are this rating and I've seen them in other low stress applications. The 5/16" bolts that hold my air cleaners to the carburetors on my BN1 are also a "B" rating with the "WODEN" vendor name.

D - 45/55 TONS TENSILE, I've seen this listed as 45/55 TT but this would make it the same as the higher R rating which doesn't seem to make sense. I have at least one bolt in my collection labeled "BEES 45D55."

P - 35 TONS TENSILE, This seems to fit the pattern and this is referenced somewhere in my research but I don't have any examples. I would suspect that this SHOULD be a 35/45 strength rating. I've also never seen a "P" rating code on any bolt.

R - 45/55 TONS TENSILE The most common rating code for fasteners on my BN1 and seems so be on most period cars through the end of the 1950s. I have plenty of bolts labeled "BEES 45R55. According to Phillip Brown at British Tools & Fasteners, this is roughly equal to a U.S. Grade 5.

S - 50/60 TONS TENSILE, The S rating appears to have replaced the R rating around 1960 and as you can see it's slightly stronger. I have a bolt in my collection labeled "RUBERY OWEN S50-60"

T - 55/65 TONS TENSILE, I have a bolt labeled "BEES 55T65"

V - 65/75 TONS TENSILE, Once again I have an example labeled "BEES 65V75"

I also found a bolt on my three speed transmission with the markings "SPARTS HT SAE" One of the few non BSF (Whitworth) bolts on the transmission and I believe that the HT stands for High Tensile, but that's just a SWAG. I have found other bolts labeled HT in high stress areas on the suspension of my '60 Bugeye.

With regard to the information above and its comparison to SAE Grade 5 and Grade 8 here is what my research has come up with.

I believe that the first number on the British bolts, may be the Yield Strength, which is defined as:

The maximum load at which the material exhibits a specific permanent deformation.

The second number most likely represents Tensile Strength, which is defined as:

The maximum load in tension (pulling apart or shearing) which a material can withstand before breaking or fracturing.

Once again these are SWAGs on my part.

SAE Grade 5 has a minimum Yield Strength of 92,000 psi and minimum Tensile Strength of 120,000 psi for bolts 1/4" to 1" in size.

SAE Grade 8 has a minimum Yield Strength of 130,000 psi and minimum Tensile Strength of 150,000 psi for bolts 1/4" to 1" in size.

Therefore, for an "S" rated British bolt with a rating of 50-60 Tons Tensile, or 100,000 to 120,000 psi, this closely matches the Grade 5 and an "R" rated bolt at 45-55 Tons Tensile, 90,000 to 110,000 psi is also close to a Grade 5.

A "V" rated bolt with a rating of 65-75 Tons Tensile, 130,000 to 150,000 psi, matches exactly the Grade 8 specifications.

Of course I used a standard U.S. ton measurement of 2,000 lbs., but a British Ton is 2,240 lbs., which should make the British bolts that much stronger, which I know from personal experience that they're not. Reference the term "British butter bolt."

Yes, I know, too much information. Comments?

Cheers,

Curt

[Healey]

Hi All,

I have a correction to my initial post with regard to the definition of "Yield Strength." It should read "The minimum" load at which the material exhibits... NOT the maximum load.

"I believe that the first number on the British bolts, may be the Yield Strength, which is defined as:

The maximum load at which the material exhibits a specific permanent deformation."

Cheers,

Curt

[murphy stout]

Yes, that would be a big difference
Thanks for the info!

[sandytest2000]

go and get "fastener black book" it contains every bit of information about fasteners.

[BTF]

Attached is a "tensile grading chart" for BSW and BSF threads.

Note that Grade R bolts are only available in BSW and BSF threads

AND

Grade S bolts are only available in UNC and UNF threads.

Upon checking our inventory in house, I can confirm that we only carry Grade R bolts in BSW and BSF threads.