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OK....here we go......

When the box of the Dodge got replaced, they had to re-install my Reese gooseneck rails. The body shop used the grade 5 (I believe) bolts for this.

Should I replace these with grade 8 bolts?

I wanna make sure everything is as safe as it can be....so what grade bolts get used in installing the rails???




:bubbakevin:bubba
 

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Built Not Bought
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better safe than sorry grade 8 all the way.
 

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If you can snap/sheer off a grade 8 bolt i give props. I dont see one streching but heck im new here so teach me what are the pros and cons of using grade 5vs grade 8. for a hitch
 

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I understand i myself use a pin for my hitch. As for gooseneck hitches homemade/kit i see alot of people/kits using at least 4-6 grade 8 bolts thats all i was trying to say
 

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I understand i myself use a pin for my hitch. As for gooseneck hitches homemade/kit i see alot of people/kits using at least 4-6 grade 8 bolts thats all i was trying to say
Yup I agree, That is why I said do what the manufacture recommends. They should have the engineering and insurance to back up their claims.

I just see way to many times where people use the old myth's.
Bigger is better, tighter is better, make it thicker it will hold and so on. Where as the best is an educated, engineered solution.
 

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Im with Doug on this one I would call the hitch manufacturer and get the same grade they use.
 

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Depending on how you are using the fastener, you would look at the appropriate and corresponding strength type. For example, bolts that attach a D-ring bracket to the bumper face of a vehicle would be critical in tension . So you would want to know what the tensile strength a particular bolt is. Bolts that attach winch-mounting plates are typically seeing mostly shear loads thus preventing the winch from departing from the vehicle during winching operations. In that case, shear strength is important to you.

Mark’s Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8’s as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, someone can figure out how much load that fastener can carry in both tension and shear.

Using a .250-inch diameter grade 8 fastener gives you the following shear capability:

A = Cross-sectional area of the fastener size (since bolt bodies/shanks have circular cross-sections, use area of a circle) = Pi x r2 where R (radius) = .250/2 = .125, therefore A = Pi x (.125)2 = .0491 square inches (in2)

Capability in shear = 91,000 lbs / in2 x .0491 in2 = 4468 lbs

Using the same .250-inch diameter grade 5 fastener results in the following:

Capability in shear = 75,000 lbs / in2 x .0491 in2 = 3683 lbs

That’s a difference of over 750 lbs or over 1/3 ton. In this example you can clearly see that using a grade 8 fastener has a superior advantage over the grade 5. Therefore the result is if someone is using grade 5 bolts in a shear application like the winch plate example, they will fail almost 800 lbs earlier.

I’ve also heard the argument that grade 8’s are more brittle than grade 5’s and that’s why you shouldn’t use them. Well, first you need to understand what the term “brittle” really means. Brittleness in bolts is defined as failure at stresses apparently below the strength of the bolt material with little or no evidence of plastic deformation. Typically, fasteners are not brittle below 180 ksi ultimate tensile strength. Grade 5’s have an ultimate tensile strength of 120 ksi and a grade 8 fastener has an ultimate tensile strength of 150 ksi. This is why brittle is a relative term. Nearly all fasteners are considered ductile except some made from PH 15-6 Mo, 17-4 PH and 17-7 PH.

Going back to the D-ring on the face of the bumper example, you would want to know its tensile carrying capability. Calculating the tensile capability is not as easy as shear since the thinnest portion of the bolt is at the minor diameter of the threads (bottom of the thread “V”). So you need to know the nominal minor diameter of that particular fastener. That’s where military specification MIL-S-8879C comes in. It is titled “Screw threads, controlled radius root with increased minor diameter, general specification for”. It lists that and a lot more for almost all possible fasteners. MIL-S-8879C lists the nominal minor diameter of a .2500-28-UNF at .2065 inches. We can now calculate the A (area) of the cross-section:

A = Pi x r2 = Pi x (.2065/2)2 = .03349 in2


Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum

Grade 8 bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum

Grade 5 bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum
Grade 5 bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum

Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.
 
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wow Fasst thats the kind of stuff we need. that definitively answers the question, without the old wives tales. good job.
 

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somone mentioned call the manufactuer, and seeing what they recommend. i would say thats sound advise. having said this, i will cast a vote for grade 5. as many on here know, this question [a similar one] was asked a short while back. i have asked dealers who install for a living the same question, they recommend grade 5. in the last thread i posted how i wanted to uprgarde from a 5 to a 8 in one of my trucks rear bumpers. well i did an upgrade approx two months back on the wheel of one of my big tractors. over the course of three years i have had issue's with the right side wheel of my international tractor slideing outward towards the end of the axle. [this tractor has dual wheel capabilities] therefore the wheel is held on with a dual clamp type system[ looks like a half moon] thats held in place with 4, 5in long 7/8 bolts. anyway , when i originaly discovered this issue, one of the three grade 2 bolts were missing, and the others were loose[should be 4]. after tighting the best i could with a cresent wrench, i limped it a mile back to the truck. well it got loose along the way again, and bent one of the three bolts. long story short, i upgraded to grade 8 and watched it like a hawk for the next two months, they came loose while i was headed to the field last week. instead of bending, two of the four bolts broke, allowing the wheel to become dangerously loose, therefore limping home wasnt an option. i fixed the issue with 4 new grade 5's, and a bottle of locktite. i use to blindly support grade 8 hardware for anything i wanted to be sure of holding. grade 8 has it's purpose, but it's not a fix all.
 

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... i fixed the issue with 4 new grade 5's, and a bottle of locktite. i use to blindly support grade 8 hardware for anything i wanted to be sure of holding. grade 8 has it's purpose, but it's not a fix all.
but you've changed the scenario by adding locktite to the equation....
 

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how so? the locktiite is simply keeping the bolts from becoming loose. [so far] it has come loose wether the bolt was an 8 or 5, twice while running 5's, which only bent. the one time i ran 8's they didnt bend a bit, they broke.
 

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it's easier for a loose bolt to break than a tight one - stress will fatigue a fastener rapidly. so, more than likely, had you locktite-ed the grade 8s, they'd be holding fine now.

guess it doesn't really matter - whatever you're using is working.
 
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