Re: Grade 5 or Grade 8??


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Posted by Andy T on September 22, 2000 at 23:11:27:

In Reply to: Grade 5 or Grade 8?? posted by Tex on September 22, 2000 at 08:35:50:

Without getting carried away.... Grade 5 will suffice in all, but the highest stress applications. The key thing to any grade bolt is torque. Too little and the bolt will loosen on it's own. Too much and the bolt will stretch beyond it's yield strength. It then loses it's ability to apply clamp load to the pieces it's holding together, and agian it will loosen and/or fail. Grade 8 bolts are stronger and although they are harder when properly torqued they withstand shock loads better. Such as holding a tow hook to a frame that will be jerked by a chain or strap. DO NOT use lock washers in critical applications. They are a hoax! I know many, many OEMs stil, use them. The SAE stopped recognizing them about 30 years ago. I can probably find a good report on that if anyone insists. Use locknuts or better yet Loctite. 242 or 243 is good for everything on our trucks. Good grade 5 bolts will serve you well, most of the fasteners on our trucks are oversized and that is to our benefit. Just don't get carried away when you tighten a bolt. A 3/8-16 grade 5 bolt only needs only 30 ft/lbs of torque. If you use antisieze, like I do on everything, you need to reduce torque 40%. Regards, Andy Tierney


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