Hardened bolts or not

[emr]

I need to get a pintle hitch for my pickup truck. I am probably going to get a the two part hitch and put it together myself. I am going to get the part that goes into the receiver and the pintle hitch separate and then bolt the pintle hitch onto the other part.... anyway, should I use hardened bolts for this or should I just use regular bolts?

p.s Sorry for starting such a lame thread.

 

[rskybiz]

Hardened!

 

[SkwerI]

I'd say Grade 8. The bolts holding the pintle ring on my trailer are grade 8, as well as the bolts holding my hitch to my truck frame.

 

[NeTree]

Grade 8 all the way. Anything less doesn't meet DOT specs anyways.

 

[PCTREE]

Hardened and preferably from a US manufacturer. ALL the bolts on Wraptors are US made as I am told by reliable sources that imported stuff is not to be trusted as their quality control aint worth squat

 

[emr]

Are hardened bolts more brittle than regular bolts?

 

[SkwerI]

Yes, but you will have them securely tightened. And the total shear strength of all four bolts combined is much higher than many other parts of the hitch.
My 30,000 lb pintle hitch that came on my bucket truck was held on with six grade 8 bolts.

 

[NeTree]

Are hardened bolts more brittle than regular bolts?

No.

 

[Stumper]

I agree that grade 8 bolts are appropriate for the application but in the FWIW category.... In applications where vibration and shock loading are resulting in grade 8 bolt breakage grade 5 can actually prove more durable. The grade 8 has greater absolute strength but it is relatively brittle. Grade 5s are high tensile strength (though less than grade 8 ) with greater ductility.

 

[sawinredneck]

I'm with Justin, on the big splitter build, I used grade 5 bolts to hold the push block together. Two reasons, grade 8 just snaps and shoots shrapnel everywhere. Grade 5 will flex and bend, yes, they do snap, but you have some warning they are getting ready. In many instances I'd go the other way, a pintle hitch being one. If the bolts are tight, little to no force is applied to them and if they snap, something WRONG happened!
It's about knowing what you expect from the bolt, and applying the right bolt in that application. In this case, go with grade 8 and be happy!

 

[emr]

Thanks much fellas.

 

[bruce6670]

Is a grade 8 bolt hardened ? Is that what makes it stronger ?

 

[NeTree]

Yes and yes.

 

[sawinredneck]

It's also what makes it weaker in some applications, grade 8 allows for little to no flex or side load. It's hard to explain, a grade 5 bolt will take more stress over time than a grade 8, but the grade 8 will take more force on a one time load.
Basically, loads of a predicted amount, on a continuousness use, grade 5 because they will flex, but lack the side shear of the grade 8.
Something with no flex or side loading, grade 8. The grade 8 will take, easily, three times the sheer load of a grade 5, but it's so stiff it will not flex, it snaps.
Does that help at all?

 

[NeTree]

No, because your thinking is flawed.

 

[sawinredneck]

OK, why?

 

[HolmenTree]

Grade 8 takes a alot more torque then the lower grades too for secure tightening. Grade 5 nut on a grade 8 bolt is still much better torquing then both grade 5 nut and bolt.

Willard.

 

[NeTree]

Because you're not accounting for "yield strength". If a grade 5 deforms and a grade 8 snaps in a given application, you don't have the proper size bolt to begin with. It's incorrect to presume that the grade 5 is performing better; it's not. It's just that the grade 5 bolt has a lower yield strength (the maximum force that can be applied before the metal permanently deforms). Once you reach the region of plastic deformation in the bolt, it might as well not be there. All that "give" is for naught.

In applications of repeated shock-loading, every time the load deforms the bolt a little, there's a little more slack to make the next shock load deform it more, and more, and more. A properly-sized and graded bolt will hold the load securely to prevent this.

 

[sawinredneck]

I won't argue anything you said, but in a given circumstance, the deformation, will keep things together in applications, where the snapping off is the end of operation in others.
As I said with the splitter, grade 8 would snap easily, and could be dangerous, grade 5 will flex and is more tolerant or this.
In a situation with side load, the grade 8 wins every time, the shear strength is unbeatable. Put some flex in, and it will snap, where the 5 will put up with it. Eventually it snaps, but is more tolerant.
With out a shock load, I can lift my F-150 off the ground with a single 1/4-18 bolt easily, grade 5 or 8. Yes, I am all for the right bolt for the right job, and in this case it's grade 8, no doubt! But if there is a side load or a shock load, other factors need to be considered!

 

[NeTree]

And again, if you need the bolt to deform to "keep things together", you don't have the right size bolt. That flex IS a failure, Andy. Believe it or not, grade 8 bolts flex, too; but the higher yield strength means it takes more force to flex them, and unless you breach the (higher) yield strength.. they'll spring right back.

Did you mean 1/4" x 20 or 1/4" x 28? Never heard of 18 tpi.

 

[Old Monkey]

What about two grade 5's and two grade 8's?

 

[NeTree]

Wouldn't that be equal to one grade 26?




Why? If the two grade 8's snapped, you'd have two (weaker) grade 5 bolts holding the twice the load. If the grade 5's just deformed (and didn't break), then the two grade 8's are still holding twice the load. Use four proper-sized grade 8's, and they all hold the load without deforming. If you happen to break them all off, you probably have other things to worry about just then.

 

[Old Monkey]

Why? Mainly because I have no idea what I am talking about but didn't want to be left out of the discussion.

 

[NeTree]

No sweat, Darin; it's a valid question regardless, and something I have seen done.

 

[sawinredneck]

1/4-20, sorry.
I'm just saying deformation and retraction is alloted in MANY engineering applications, such as the skin and airframe on your airplane. That airplane acts much like an arrow in flight, just on a larger and slower realm, but the flexing and bending are still there, the entire plane is "quivering" as it flies through the air. You want grade 8 rivets on that? You want 8085T6, or 6061T6?