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Keep in mind in some cases a grade 5 is better then a grade 8 because gr8 bolts are hard and are ment to have high tensile stregnth, but are more prone to shearing, a grade 5 is softer but has some "give" in it and wouldnt shear where the harder gr8 will.
Read the link below, grade 8 is ALWAYS better than grade 5. However, the engineers at the auto companies build to a specified strength, no more as any extra would cost more (even a few pennies adds up over thousands of vehicles). ROCKCRAWLER.com - Grade 5 vs. Grade 8 Fasteners
If you're torquing a 1/2-13 grade 8 bolt to 150 foot lbs, its likely overtightened and failing because of that. I have a print out of the chart in the following link and have used it without and problem so far. Note the difference between plain, plated, and waxed (oiled?) bolts. Proper Bolt Torque - by Zero Fasteners
Read the link below, grade 8 is ALWAYS better than grade 5. However, the engineers at the auto companies build to a specified strength, no more as any extra would cost more (even a few pennies adds up over thousands of vehicles). ROCKCRAWLER.com - Grade 5 vs. Grade 8 Fasteners
If you're torquing a 1/2-13 grade 8 bolt to 150 foot lbs, its likely overtightened and failing because of that. I have a print out of the chart in the following link and have used it without and problem so far. Note the difference between plain, plated, and waxed (oiled?) bolts. Proper Bolt Torque - by Zero Fasteners
Great Article tecgod, it explains a lot in a short article.
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