this is the end cap of about 4 aisles of bolts and nuts at my local hardware store. 2.7 miles from my shop. Way too close.
Are Grade 8 bolts overkill for the front bumper?
- Thread starter UKTJ
- Start date
this is the end cap of about 4 aisles of bolts and nuts at my local hardware store. 2.7 miles from my shop. Way too close.
I am sure OP can source them in UK but its actually finding a specialized fastener supplier like I did in OZ.
In fact The Boogieman found a link for me to an Australian supplier, Cookies and IP address send you where "they" want you to go when online.
Twice now USA members have given me links to Australian websites that were not showing up on local searches.
I come from a long line of steel erector's/Boilermakers and I know for sure you can get all the imperial sizes in UK but they are just hard to find if you dont know where to look.
In fact The Boogieman found a link for me to an Australian supplier, Cookies and IP address send you where "they" want you to go when online.
Twice now USA members have given me links to Australian websites that were not showing up on local searches.
I come from a long line of steel erector's/Boilermakers and I know for sure you can get all the imperial sizes in UK but they are just hard to find if you dont know where to look.
I'd skip grade 8 unless called for in the specs. Break one of those brittle bolts and they are impossible to drill out.
If you're worried, tack weld it. It's easier to grind a weld then drill out a grade 8.
If you're worried, tack weld it. It's easier to grind a weld then drill out a grade 8.
Last edited:
Were these going into a threaded piece? I missed that.
a little trick to drill gr8 is to heat them a little. Get the material over 500f and it will anneal. A hss bit will drill it with ease. A cobalt bit will drill gr8 but it takes patience.
The bumper bolts never see shear loads. If they do, the connection has failed.
I respectfully disagree. Bearing capacity of the bolted system is absolutely a part of the strength of the system, and should be part of the design except in cases where slip is unacceptable. A bumper to frame connection is not a slip-critical application, and bearing on the bolts is acceptable at the highest forces.
Painted/coated steels generally have a coefficient of friction of anywhere from .10 to .25 against other painted steels.
The clamp load of a properly torqued SAE Grade 8 1/2-13 UNC bolt is 12771 lbs, and 9046 lbs for Grade 5 according to Fastenal, which uses a designation of preload being 75% of proof load.
If we give the painted steels a relatively liberal coefficient of friction at 0.25 (the only way to know would be actual testing of powder coated steel on the bumper paint), each Grade 8 bolt only generates about 3200 lbs of friction-resisting force, and Grade 5 about 2260 lbs.
With a 12,000 lbs winch stalled out (4,500 lbs of shear per top bolt, 3,000 reaction on each lower bolt), both the Grade 5 and the Grade 8 top bolts would allow the joint to slip and place bearing force on the bolts.
Start pulling on either one of the recovery points (no winch load) and as soon as the tension on the recovery point exceeds 6400 lbs at any instant, and the bottom bolted joint switches from friction to bearing force. And that’s for Grade 8. Grade 5 would slip and enter bearing at 4500 lbs on the recovery point.
Meanwhile the bottom fastener itself can resist shear up to 9,800 lbs, or an expected failure at 19,600 lbs of pulling on the recovery point. As the bolt stretches elastically or plastically, the actual tension is reduced and the bolt is almost entirely in shear loading.
In bolted connection design, the shear strength of the bolt is generally not assumed to be reduced regardless of whether the joint is snug tight or fully tensioned. Laboratory tests used in development of structural bolting standards show that the presence or absence of a bolt preload has no significant effect on the ultimate strength of the bolt either in tension or shear.
Friction forces on the head of the bolt to the top plate are generally ignored, as the bolt usually has a small capability to misalign in the hole. Given that TJ frames have welded nuts, this may add a small amount of frictional strength, but this cannot be relied upon to keep the joint in friction versus bearing. I doubt the welded nuts are sufficiently stiff to resist misalignment at high forces.
That said, bumper bolts are indeed intended to be installed as fully tensioned and not snug tight (typical in steel erection), and the friction of the bumper to frame is indeed an intentional part of the design. If the bolts were merely snug-tight, the bumper would be free to slip around due to the clearance gap between the bolt and the hole, and would create unnecessary stresses.
The friction is the primary means of retaining the bumper and recovery points at low to moderate forces, but the bolts themselves also have the capability to resist shear, especially in higher load applications.
Last edited:
Since a heavy-duty winch comes with Grade 5 hardware which is well proven to be strong enough, I don' t see any need for a bumper which does not carry the winching load of the winch to require anything stronger than Grade 5 (or 8.8).
Perfectly accurate until you toss in the fact that most TJ front bumpers are held on with at least 4 bolts through tow hooks which I would really prefer to have gr. 8 hardware.
I am however confused by your statement of the bumper not carrying the winching load. Is that based on the presumption that a winch deck other than the bumper will be in use?
No, it's because a winch is bolted to the frame under the bumper, the winch mounting bolts only pass through the bumper. The bumper isn't even required to be present to mount a winch.
I'm not talking about my Savvy bumper with its integrated winch mount, I'm talking about the factory bumper and most aftermarket bumpers that require winch mounting plates.
You are in an argumentative mood this morning aren't you. Not interested in getting into a pissing contest, not many bumpers have integrated winch mounts.
Not at all. You keep refuting my statements even though I give you an out. It isn't a pissing contest, I specifically mentioned other than bumper mounted winch decks to stop you from making absolute statements with holes in them big enough to drive a semi through. Then I highlighted that part to see if you missed it somehow.
Now, now children. Communication is key! Without taking either side: clear writing and thorough reading/comprehension is essential.
Lots of obsessing over nothing in this thread. On the bright side, things are so good in the US that we can spend crazy amounts of time arguing over trivial stuff that really isn’t that important.
For my $2 (inflation…what’s a penny?), I use grade 8 whenever possible but if not available for whatever reason, I’ll use grade 5. I use stainless bolts and nuts for anything non strength critical. Don’t use stainless for anything that needs to be strong!
Don’t over think it. Many people never even take their Jeeps out of the parking lot so those people could use stainless or below grade 5 and never have an issue.
For my $2 (inflation…what’s a penny?), I use grade 8 whenever possible but if not available for whatever reason, I’ll use grade 5. I use stainless bolts and nuts for anything non strength critical. Don’t use stainless for anything that needs to be strong!
Don’t over think it. Many people never even take their Jeeps out of the parking lot so those people could use stainless or below grade 5 and never have an issue.