Stainless Steel Bolts-How Strong

[CROW]

Fifth wheel hitch mounts flush on the truck bed and is held with eight bolts. I will be removing and reinstalling to fix rust on the bed and hitch. Bolts are Grade Five, 2" long (not counting the head) and the threads are 1/2 inch across. The head of the bolt is 3/4". Have a chance to replace with stainless steel bolts at the "right price", but wonder how strong a stainless steel bolt that size would be. There may be grades of stainless as well for all I know. There is some rust on the threads of the bolts where they go thru the hitch into the actual mount which is located on the frame below the bed.

Thanks in advance for any responses.

 

[GAmes]

Is your 5er worth less than a set of new grade 8 bolts? Mine have never rusted.

 

[PToombs]

Most hitch and body manufacturers use grade 5 hardware because it will stretch and give in an accident. Grade 8 breaks due to the hardness.



If you can find stainless in the right grade, I don't see a problem with that. The other option is to smother it with never-seize upon installation.

 

[jelag]

Stainless fasteners are softer than a good plated grade 5 bolt...

Stainless fasteners are used in food grade, and other industries where no rust is acceptable and different grades of stainless are used in different locations.....

When I was working years ago making pressure vessels for the food industry we made both mild steel and stainless... . the stainless were used in high acid locations where there was a lot of tomato's etc... .

On the average the same system using mild steel lets say had 5/8" bolts, the stainless system would have 7/8 or 1" fasteners doing the same job... . they needed the extra diameter to get the same working load... .

If I use a fastener where it can be seen its plated... . if where no one will see it... . than its the correct grade for the strength required and lathered with anti seize at the time of installation...

 

[WilsonF]

If you do go to s/s you need to use anti seize or some other thread lubricant, the threads will easily gull with s/s then you've got problems.

Floyd

 

[CROW]

Thanks to all for your responses. Think I will purchase new Grade 5 bolts since that was what was used by the manufacturer but when reinstall will use anti-seize. These types of bolts are not too expensive.

 

[jkalchik]

If you have a torque spec for those bolts, it's probably a dry spec. Using any kind of lubricant (grease, anti-seize, etc. ,) reduce the torque by 10-20%.

If the original bolts were grade 5, go with that. A grade 8 bolt will hold where a grade 5 bolt will have already failed, but that may have other (potentially really undesirable) consequences.

 

[LandShark]

The only time a grade 5 bolt is better than a grade 8 is in cost and in the rare case when you want a bolt to fail at a certain point. In a situation where you want the highest strength, a grade 8 bolt will always be better than a grade 5 bolt.
Stainless bolts can be as strong (or stronger) as grade 8, but they are often not clearly marked, so you may not know what you are getting. If you want stainless, buy from a reputable place and get the specs for what you are buying.

 

[steved]

The only time a grade 5 bolt is better than a grade 8 is in cost and in the rare case when you want a bolt to fail at a certain point. In a situation where you want the highest strength, a grade 8 bolt will always be better than a grade 5 bolt.

Not true... a grade 5 will have more tendency to stretch/bend under load, where a similar grade 8 will fracture. Grade 8s are strong, but brittle at the same time. That's the main reason to use a grade 5 in place of a grade 8... a good grade 5 will actually withstand more abuse.



Grade 5s have their place, just as grade 8s do... if grade 8s were the answer for everything, why use a grade 5 for anything (they only cost pennies more per pound)??? Its because each have certain characteristics that are desirable over the other.

 

[DPellegrin]

I'm going to have to agree with jkalchik and landshark on this one. steved I would recommend you look at the definition of "tensile strength". Grade 8 bolts are regularly used in high strength applications. You will find them on truck frames attaching the crossmembers and you always find them attaching the 5th wheel assemblies on Kenworth and Peterbilt trucks. My recommendation would be to go to your nearest Caterpillar tractor dealer and buy what CAT would call grade 8 bolts. Of course they are going to cost significantly more but you get what you pay for. Caterpillar Tractor Co. are the metallurgists of the world and have developed their fastener technology to an advanced level. I have good experience with CAT fasteners where other brands and grades have failed.

 

[steved]

I have seen places where a grade 8 failed a long time before the same size grade 5 failed... grade 8s cannot take shock loading, they will snap. I have even seen literature on suspensions stating to not use grade 8, and specify grade 5 for that reason.



Again, grade 8s have their place, grade 5s have theirs... and neither are really that interchangeable. And again, the price between a 5 and 8 is pennies on the pound.