[Fot] Have you ever wondered?

[vfracing at aol.com]

FRIENDS:Have you ever wondered what those little letter marks mean on the heads of bolts in our Triumphs (and other British cars)? You know, the letters at the bottom, below the manufacturer's name (Rubbery Owen, etc.).  Well, I did as well when looking at the best way to secure the cam sprocket to the camshaft. Those letters designate the minimum tensile strength of the material in the bolt, just as the hash marks do on the heads of SAE bolt.  So I put together the attached handy chart showing what the marks mean.  I threw in some Metric as well, just for fun. When you go to the store you can pick the proper (or stronger) grade of bolt to replace the 50+ year old fasteners in your next project.  If reusing the original fastens, which are perfectly fine for many applications, you will be sure not to mix up the fasteners from one application to the next (using a thermostat housing bolt on the cam drive could lead to disaster....).Of course, when replacing bolts with new ones it is a REALLY GOOD idea to make sure the threads are not put in shear by using a shouldered bolt.  To do this for the cam drive I needed to go to ARP and special order a 5/16-18 bolt with the proper grip length, and then shorten it so it won't bottom on the threads.  ARP part number 3AG1.250-2S (about $6 each direct from ARP)And yes, I've totally ignored the world of Whitworth.  Enjoy.
Phil Gott

| Bolt Grade | Minimum Tensile Strength (000 psi) |
|
| AN*** | SAE* | British** | Metric* | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | 180 |
|   | 2 > 3/4" |   |   |   | 60 |   |   |   |   |   |   |   |   |   |   |   |   |
|   | 2 to 3/4" |   |   |   |   | 74 |   |   |   |   |   |   |   |   |   |   |   |
|   |   | P |   |   |   | 70-90 |   |   |   |   |   |   |   |   |   |
|   |   | Q |   |   |   |   | 80-100 |   |   |   |   |   |   |   |   |
|   |   | R |   |   |   |   |   | 90-110 |   |   |   |   |   |   |   |
|   |   | S |   |   |   |   |   |   | 100-120 |   |   |   |   |   |   |
|   |   | T |   |   |   |   |   |   |   | 110-130 |   |   |   |   |   |
|   |   |   | 8.8 to 16mm |   |   |   |   |   |   | 116 |   |   |   |   |   |   |
|   |   |   | 8.8 > 16mm |   |   |   |   |   |   |   | 120 |   |   |   |   |   |   |
|   | 5 |   |   |   |   |   |   |   |   |   | 120 |   |   |   |   |   |   |
| All |   |   |   |   |   |   |   |   |   |   | 125 |   |   |   |   |   |
|   |   | U |   |   |   |   |   |   |   |   | 120-140 |   |   |   |   |
|   |   | V |   |   |   |   |   |   |   |   |   | 130-150 |   |   |   |
|   |   | W |   |   |   |   |   |   |   |   |   |   | 140-160 |   |   |
|   | 8 |   |   |   |   |   |   |   |   |   |   |   |   | 150 |   |   |   |
|   |   |   | 10.9 |   |   |   |   |   |   |   |   |   |   | 151 |   |   |   |
|   |   | X |   |   |   |   |   |   |   |   |   |   |   | 150-170 |   |
|   |   | Y |   |   |   |   |   |   |   |   |   |   |   |   | 160-180 |
|   |   |   | 12.9 |   |   |   |   |   |   |   |   |   |   |   |   | 177 |
| Sources:  *Bolt Depot Inc. and **Trojansf.co.uk/technical/fastener-grades and ***Skyshop |
|

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