What grade of hardware to mount seats?

[Primered_69]

What grade of bolts to mount seats?

[Randy70C-10]

Depends, are you over-weight? (kidding) I'm not sure but I do know that you can never go wrong with grade 8. But then, you floor would give out before the bolts would.

[CHEVYE]

i would grade 8 it too. no reason to skimp on 6 or 8 seat bolts.

[N2TRUX]

Actually in this application grade 5 might be best. I'm sure someone will disagree, but let me at least explain may answer. A grade 8 bolt is stronger than a grade 5 bolt in certain applications. If the bolt is used in an application where it will be subjected to stretch (like a connecting rod bolt) then a higher grade is better because it will stretch less than a softer grade bolt. On the other hand if a bolt is used in an application where it is subjected to "shear" force as the case would be in the event of an impact in your truck, a softer bolt will stretch more than a harder bolt before it fails.

Ok, now y'all can prove me wrong....

[LUV2XCLR8]

I used all SS ones on mine, go figure

[Randy70C-10]

What N2TRUX said actually does make sense.

[4tiresngas]

I say Grade 8, and I for one do not want to test N2TRX's theory. If anybody else tests it, let us know...lol Also be sure to post your remaining salvageable parts on the parts board.

[longhorn71]

Originally Posted by N2TRUX

Actually in this application grade 5 might be best. I'm sure someone will disagree, but let me at least explain may answer. A grade 8 bolt is stronger than a grade 5 bolt in certain applications. If the bolt is used in an application where it will be subjected to stretch (like a connecting rod bolt) then a higher grade is better because it will stretch less than a softer grade bolt. On the other hand if a bolt is used in an application where it is subjected to "shear" force as the case would be in the event of an impact in your truck, a softer bolt will stretch more than a harder bolt before it fails.

Ok, now y'all can prove me wrong....

I disagreed with you at first.Then i thought about it and relized that does make sense.That is what i love about this board you learn something new everyday!!Got to head down to the parts store and replace the seat bolt in my truck tomorrow!!Thanks for the great in put Ken

[4X4GMC1972]

Grade 8 bolts have a higher yield and tensile strength, basically meaning the grade 5 bolt will break before the grade 8 will. A grade 8 bolt is stronger in all applications.
For mounting a seat, a grade 5 bolt will provide more than enough strength as long it is tightened properly. The sheet metal on the seat frame or the floor will rip out before the bolt would shear.
BTW the seat belt bolts are grade 8.
Todd

[Longhorn Man]

Originally Posted by N2TRUX

Actually in this application grade 5 might be best. I'm sure someone will disagree, but let me at least explain may answer. A grade 8 bolt is stronger than a grade 5 bolt in certain applications. If the bolt is used in an application where it will be subjected to stretch (like a connecting rod bolt) then a higher grade is better because it will stretch less than a softer grade bolt. On the other hand if a bolt is used in an application where it is subjected to "shear" force as the case would be in the event of an impact in your truck, a softer bolt will stretch more than a harder bolt before it fails.

Ok, now y'all can prove me wrong....

I used to argue this exact same point...and N2TRUX is 100% right.


Besides...here's the part that makes it all a moot point... put on your seat belt, and don't worry about it. (onless you did a late model seat swap with integrated 3 points belts...which then you are probably screwed anyways come accident time) your SEAT BELT is what's going to hold you down...not the seat.

Grade 5 HDWR is overkill for 90% of the automotive needs in any aplication you can find. I'll have to dig out the specs of the bolts sheer strength.

If you think about it...it makes perfect sence. A grade 8 DOES have more clamping force... but in order to do this, they are stiffer and more specific to the clamping loads. Sheer loads, you need something that'll give a little bit. (not measureable by you or me) If it is too rigid, it'll shatter.

N2TRUX...I got flamed for this for almost 2 years, and actually get hate mail every time I brought it up. (still get PM's w/ppl callin me an idiot becouse they disagree....friggen f-tards) So know what you know....but you may be better off knowing it quietly. Much less stressfull this way.


To keep the "You are a stupid retarded idiot" e-mails to a minimum...I'll just say get the grade 8 bolts....and the seat will stay put when you slam into the guy infront of you.
Now for the hate mail statement...
Bummer the improperly installed late model 3 point seat belt that was installed wasn't done right and ripped through the floor 1/5th of a second before your teeth went into the steering wheel.

[Huck]

As much as I hate to agree with my buddy, Andy he is right. Who gives a crap if the seat breaks loose because the seatbelt is the only thing between you and the great outdoors!! If you have a truck and the seat/seatbelt holds you in place, then you get to wonder about that 21 gal of fuel--vapor sitting right behind you. Now that is something to fix before the seat bolts!!! A side impact, a roll onto the drivers side with a bit of a slide---even with a seat belt and #8 Bolts will put you on the barbacue!!
Care to guess what grade of bolts hold the seat frames to the seat mount brackets---actually it doesn't mattter but they are not grade 8. Move your tank to the back, get some late model S10 3 point belts, then any bolt will do--I'd go with #5s as they will hold that seat just fine. (:>)

[Tx Firefighter]

Michael, you can buy grade 8 hardware at Tractor Supply for 3 bucks a pound, any size bolts, nuts, washers, or whatever. Just grab handfulls of whatever looks handy. Personally, I use them in everything. I have my own opinions about strength and besides, the grade 8 bolts have an excellent cadmium finish on them that keeps corrosion away for a long time.

[69 longhorn]

grade 8 bolts are stronger in both stretch & shear, as compaired to a grade 5 bolt. I dont have the link, but somebody put one up a yr or so back(Tom Hand, i think). at any rate, with that said......I dont beleive you need more than a grade 5 to hold the seats in(as already said, the floor will rip before the bolt fails!). there is no doubt in my mind that the grade 8 would be stronger tho....... L

[chipflyer]

If you want grade 8 bolts get them, its probably overkill. Take a look at what GM originally used to hold seats down, bolts with no marks are grade 2, 3 marks are grade 5. Never saw a grade 8 from GM that held a seat down, seen lots of 2's and 5's though.

[69 Short Fleet]

I'm surprised no one has touched on the threads themself. Rolled threads give the bolt itself a higher degree of integrity and are less prone to fail (this of course is usless IF the bolt is not the propper grade for its application). This is why F-1 & Indy (not sure on NASCAR as I don't follow it) uses them on alot of there applications however they are made from high grade titianium. Installation proceedures & torque are compulsory. High end exotic materials & design were first used (and still are) in the aviation & military & filtered down (for lack of a better word) to the racing industry. The old school (& I mean the REAL OLD SCHOOL not the 1986 Honda fart can type "R" tuners) NHRA crew chiefs relied heavily on military & air force specs as this was an invalueable tool for them to set standards & learn. Bolts / nuts hardware are actually very sophisticated and a lot of engineering goes into them. I have never seen any markings on the seatbelt bolts (for our trucks) so I don't have a clue what the actual grade of them is (good question). I personally have a higher concern with the integrity of the buckles/latches or the return mechanism failing on SOME of the original seatbelts from repeated use, as I have actually never took one apart to look at it. As mentioned though I think a part of the floorboard would come with it bolt upon heavy impact on some of these old girls (lol). Doug

[mocwon]

69 Short Fleet; oops.... guess I should have read your post before posting my reply....



I started to post this last night and then deleted it. I believe these bolts are 5/16 X 18. Grade 5 bolts of this size (what GM used from the factory for this application) have minimum tensile strength of 120,000 PSI and grade 8 150,000 PSI. There are a lot more factors to consider other than the grade of the fastener such as proper torquing, rolled threads vs. cut threads, the condition of the threads, whether a washer is used, how many times a fastener has been used and re-used, etc. The stamped metal seat bracket would likey tear through the bolt head before either a grade 5 or grade 8 bolt would fail. One thing is for sure, don't use bolts with no head markings like Home Depot and Lowes sells since these are grade 2 bolts with about half the tensile strength of a grade 8 bolt.