Grade 5 bolts OK for trailer hitch?

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Super77

Super77

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Guys, idiot-check me here.


I'm bolting a Reese class III hitch onto my FJ62. I've got six new grade 5 1/2"-20 (fine thread) bolts, plus 1/8" thick fender washers on both sides, plus a lock washer under the nut.

Question is about the grade 5: OK on a hitch? It's not going to be used for anything that would strain the rig. Mostly a 400# loaded platform, a bike rack, and maybe a small utility trailer.
 
Till you have to tow somebody out of a mudhole... I'd go grade 8 just to be sure..
 
I was told by my local RV shop that they use grade 5 on all their hitches because grade 8 was more brittle and grade 5 had a little "give" under severe shock loads . I've been towing my travel trailer for several years with grade 5 bolts with out issues. My (their) .02.
 
I have heard the same about the grade 8s being more brittle...but that's what I use for my hitch...
 
Grade 8 yields differently than grade 5. However, grade 5 will fail long before a grade 8 even in a shok situation. What they told you is an internet myth that people keep repeating. Grade 8 is stronger in every way over grade 5.
 
robinhood4x4 said:
You also have to remember that grade 8 bolts are useless unless everything is grade 8, which includes the washer and nut.
Click to expand...

Wut???

You think the washer, nut, hitch and the frame are available in grade 8?
 
I would use grade 8 and move on... no reason not to, but a few reasons why you should.
 
Guys,

Take a look at this chart or this one showing shear values for different grade bolts. They're not precisely in agreement, but they do show grade 5, 1/2" bolts as having a shear strength of just under 15,000 lbs, and grade 8 of just under 18,000 lbs. That's >3X the weight of the truck. With one bolt. There are six of them holding the hitch to the truck.

Let me say that again: six of them.

Now, I'm no metallurgist, but I'd bet a paycheck that the hitch itself will rip apart before those bolts do, grade 5 or 8.
 
Then why ask??
Grade 5 will most likely be just fine. I run grade 8 in my bumper attachment points because I like overkill. Grade 8 are also generally more consistent in their construction. Meaning lower quality bolts may not have the QA/QC of grade 8.

You are running your hitch through a single 5/8" pin as well..

Also, consider the tow straps you own and their rating.. 20K, 30K...
 
are you talking about saving 5 to 10$$$ or less on bolts? Why even go there....

I use grade 8 on my bumpers and most things that I'm concerned about staying connected or secure.

Critical items like bumpers, trailer hitches...etc that if they fail people can get hurt...would lend themselves to using the better of the two in questions of the hardware/fasteners.

I buy grade 8 stuff by the bag-full at tractor supply, and lowes when I have to, I'm sure there are plenty of other sources.

Use what you want.... but good advice here is free..
 
Mace said:
Wut???

You think the washer, nut, hitch and the frame are available in grade 8?
Click to expand...

Grade 8 is overkill, but if you're going to go through the trouble of grade 8, then you might as well do it right or at least get a grade 8 nut too. A hitch relies on the preload of the bolts providing the frictional clamping force of the two pieces, not the shear strength of the bolt. The whole idea of needing a higher grade bolt is so you can torque it higher and get a higher preload. You can't do that with a non-graded nut, you'll strip the nut.

Here's a good article on joint design, especially page 7, shear joints and clamp loads:
http://www.fastenal.com/content/feds/pdf/Article - Bolted Joint Design.pdf

Of course, I doubt most people know this and will just torque it to the normal torque or until if "feels" right.

For the OP, like has been said before, not much reason not to go grade 8 and go all the way, but grade 5 will probably be fine too. Put another way, are you going to go grade 8 bolts and then cheap out on the nuts? And like Mace said, if you're so sure of the strength of the grade 5, then why ask?

Edit: I just saw your other thread of the hitch mounted and when you said fender washers, I was thinking those thin, large diameter washer you get at home depot, not nice thick ones like you have. Those are much better.
 
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not sure why this is a ?...but when I go buy grade 8 bolts I get the correct matching washers / nuts etc, why would you do otherwise.
 
Elbert said:
are you talking about saving 5 to 10$$$ or less on bolts? Why even go there....

I buy grade 8 stuff by the bag-full at tractor supply, and lowes when I have to, I'm sure there are plenty of other sources.
Click to expand...

X2

A bag full of grade 8 bolts at tractor supply is usually less than one grade 5 bolt from the auto parts store. I also don't see any reason not to use them.

Now if they would only sell metric bolts in bulk...
 
robinhood4x4 said:
You also have to remember that grade 8 bolts are useless unless everything is grade 8, which includes the washer and nut.
Click to expand...

Mace said:
Wut???

You think the washer, nut, hitch and the frame are available in grade 8?
Click to expand...

robinhood4x4 said:
Grade 8 is overkill, but if you're going to go through the trouble of grade 8, then you might as well do it right or at least get a grade 8 nut too. A hitch relies on the preload of the bolts providing the frictional clamping force of the two pieces, not the shear strength of the bolt. The whole idea of needing a higher grade bolt is so you can torque it higher and get a higher preload. You can't do that with a non-graded nut, you'll strip the nut.
Click to expand...

There is a big difference between "It's useless unless everything is grade 8" and "The bolt and nut should be grade 8". That was my point.

Now as far as the frictional clamping forces, you are only partially correct. For the most part, yes. However, due to tongue weight, there are also extensional forces on the bolts and if the bolts stretch at all, shear strength comes into play. But honestly, if your bolts are stretching, you have way too much tongue weight.
 
I think you're fine with the grade 5's, my choice is to always overbuild, but that's just me.

One thing to remember is that there are a ton of substandard counterfeit bolts to there from china, stamped and plated, ( its a huge problem, industry wide) and for sale everywhere for cheap. If you want the real thing, with real strength, only buy from a recognized fastener supplier. And yes, they will cost more, but you get hat you pay for.
 
Overbuild it, we are talking about pennies on the dollar. Do it once and forget about it. Grade 8 is stronger in every possible way for this application... every single one. Anyone who tells your different doesn't know their stuff.
 
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