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Grade 5 vs Grade 8 bolts

Y

Yeuker

New Member
Joined
Dec 21, 2020
Messages
7
Hey Everyone,

Sorry if this has been discussed before. I read everywhere to use grade 8, 6", 3/8 bolts for bolt climbing. I believe this to be good advice, but am wondering why not grade 5? Looking at this chart:

Grade 8 vs 10.9 High Tensile bolts | Alloy Steel class 12.9 Studs

High Tensile is very strong, long-lasting carbon steel, find here the Difference between Grade 8 and 10.9 bolts and studs. Compare composition, mechanical properties, and strength.
www.hiteshsteel.com www.hiteshsteel.com

I'm not positive on how to read the above chart to please weigh in if you do. Reading this, I think a 3/8 bolt (.375") will have a shear strength of 8280 (grade 5) or 10050 for grade 8. I get it. More is better. I also get that everyone says grade 8. I also know you probably use grade 8, not grade 5.

What I am wondering is... is grade 5 also safe? If they aren't, what is it about them that makes them unsafe? Just looking to learn here from someone out there that has likely done the research on forces and torque.
 
I’m gonna guess grade 5 bolts bend easier. Idk though I’m just as interested as you. Would a grade 5 bolt hold a guy up? Probably. Would a grade 8 bolt hold a guy up? Definitely. I think that’s the most important difference.
 
While the shear strength of a bolt is used to determine its ability to hold items such as a bridge beam in place with no leverage or movement it doesn't correctly address the leverage created by inserting a bolt into a hole and applying weight to the extreme end of it. Not sure if a person could test this or if it has been tested, or if someone played with grade 8 bolts and they held and that was good enough

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Used grade 5 bolts one from time and they bent. I’m 170lbs. No issue with the grade 8
 
Yeuker said:
Hey Everyone,

Sorry if this has been discussed before. I read everywhere to use grade 8, 6", 3/8 bolts for bolt climbing. I believe this to be good advice, but am wondering why not grade 5? Looking at this chart:

Grade 8 vs 10.9 High Tensile bolts | Alloy Steel class 12.9 Studs

High Tensile is very strong, long-lasting carbon steel, find here the Difference between Grade 8 and 10.9 bolts and studs. Compare composition, mechanical properties, and strength.
www.hiteshsteel.com www.hiteshsteel.com

I'm not positive on how to read the above chart to please weigh in if you do. Reading this, I think a 3/8 bolt (.375") will have a shear strength of 8280 (grade 5) or 10050 for grade 8. I get it. More is better. I also get that everyone says grade 8. I also know you probably use grade 8, not grade 5.

What I am wondering is... is grade 5 also safe? If they aren't, what is it about them that makes them unsafe? Just looking to learn here from someone out there that has likely done the research on forces and torque.
Click to expand...
You can calculate the bending moment pretty easily - grade 5 will be beyond the point of failure in routine use (as evidenced by people mentioning that they bent them.)

Have I climbed up trees on nails and bolts that bent easily when I stepped on them in my younger days? Absolutely. Did they "work" - sure. Is it the best choice? Probably not.
 
Yeah, I agree, grade 5 would probably bend easier. Interesting that grade 5's bent on you @Jordan121787, that's pretty compelling evidence that 8's are the way to go.
 
I’ve used grade 5s and they bent! Around 200 pounds here
 
Makes sense. I forgot you guys take them back out. I preset my trees in late winter early spring so the bolts stay in. I use 5/8" x 10". They ain't bendin!
 
The harder the bolt the less bend, but the harder the bolt the more likely to snap break.
 
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