Grade 8 bolts

[kingmanbob]

It is my understanding that grade 8 bolts are superior in all applications except impact resistance. If the bolt is properly torqued, this is not an issue. If a grade 8 is loose, it will break before a grade 5, but if both grades are correctly torqued, the grade 5 will fail first.

Bob

[mobile_bob]

i would concur with your statement

bob g

[xyzer]

Another point of view..........http://www.rockcrawler.com/techreports/fasteners/index.asp
A grade 8 is one tough Bolt....under all conditions. Apples to apples if the grade 5 is loose it will fail before the loose grade 8...The grade 8 will out perform the 5 in all of the same conditions. They are not brittle try and break one! I guess my point is if the loose 8 will fail before the tight 5. I wouldn't replace all th 8's with 5's cause when they get loose they will fail ahead of loose 8's. But lets see some more feedback!

[cujet]

I do not believe there is any situation where a grade 5 is better than a grade 8.

Chris

[mobile_bob]

its been my experience that a grade 8 will work harden and crystallize if loose and break before a grade 5
grade 5 seem to hold up better if loose in practice, albeit a poor practice.

grade 5 bolts when they break off in a hole, are far easier to drill out than a broken grade 8 bolt, which seem to get as hard
as glass, especially if it is hard to get into position on.

been my observation at least.

all of this is a mute point, because a bolt should never be allowed to run loose.

bob g

[buickanddeere]

  Problem is some grade 2,5 & 8 bolts are fakes. Either too brittle or too ductile and malible.
  Either purchase fasteners from a reputable shop such as name brand auto of farm/construction machinery dealership. Bubba's bargain hardware store bolts are best left on the shelf.
  Either under or over torquing will casue fastener failure. Your torque wrench, don't leave home without it. Dirty threads, don't waste your time thinking a true torquing is going to happen.
  Loading bolts in excess shear due to worn, oversize holes or out of alignment holes will cause any fastener to fail.
  The washer(s) and nut/ internal thread are just as important as the bolt ot stud.
  True quality bolts are the AN and etc  lines sold by aircraft and race car supply shops.
 

[Doug]

I posted some disturbing pictures of 1 inch bolts sheared away from a concrete floor some time back....

The reason for the failure was a poor choice of washers and over size holes.

Doug

[phaedrus]

A tightened bolt, or a stud for that matter, is a spring in tension. It’s true that the spring in this case tends to have a narrow elastic range, but it’s a spring that’s holding stuff together, and it’s in it’s elastic range if it’s tightened properly. Obviously one ought to use the right spring for a given job. In cast iron, which isn’t particularly strong in tension, it’s particularly important to chose the right “spring” and tension it accordingly. If there were no need for gr 2 or 5 bolts they wouldn’t make ‘em.

[Quinnf]

It's a stale thread, but a good one.  Here's another viewpoint:

http://utterpower.com/engineer.htm

Quinn

[xyzer]

They have there place for sure! My 7' brush hog came with a grade 2 shear bolt on the PTO for those times when you hit a rock or a stump. It would shear the bolt if you engaged the PTO to harshly. It was always shearing the damn thing. I finally went to a grade 5 and it works great. I have sheared one and the gearbox lived through it and I hope it continues to do so. The point is I guess they are (if not fakes) alot stronger than a the other grades. If I put a grade 8 in my brush hog I would be buying gear boxes instead of bolts.
Dave

[cujet]

I have been purchasing Rockford brand bolts at Napa in Grade 5, 8 and 8.8 metric. I have serious reservations on these bolts. The half inch G5 gen hold down bolt broke upon installation. AND, it broke right at the thread/shoulder junction. Utter Crap!

The 1/2 inch Grade 8 fine thread bolts used on my car also broke right away, in the threads right under the lock nut.

Neither was anywhere near overtorqued. In fact the ones on my car were torqued with a 5 inch open end wrench!

I strongly suspect they are made in China by political prisoners.

In stark contrast, the AN hardware I have at work is tough as nails. I have never broken an AN bolt in any application. In fact, they are considered grade 5 equiv! There is a reason why race cars use AN hardware. It is not the worlds best, but it has a known load factor and yeild strength. Quite unlike the Chinglish bolts currently available.

Chris

[Tom]

You broke it with a 5 in wrench, you must have wrists the size of my thighs.  Or those are really cheep bolts. Seems like the quality of NAPA stuff is slipping lately.