Grade 5 vs Grade 8 bolts... the hot skinny!

[SPYDERLK]

Informative but not complete. You are at a big box store and choose grade 8 bolts, what nuts and washers do you get?
The nuts and washers should also be grade 8. Unless marked you will be picking up grade 2 or 5 hardware.
What if you are replacing a lower grade bolt with a higher grade, no nut to screw the bolt into, the frame is tapped?
A] You drill out the tap and use the same grade nuts.
B] You use a longer bolt to thread deeper into the blind pocket.

Washers are stamped or CUT from sheet metal. The stamping causes a slight CROWN in the washer, take advantage of the crown by placing the flat side away from the bolt head or nut.

I have found that the chine's nuts and washers much too soft for the bolts.

Nuts are not so important because theres a lot more thread root area in the engaged threads in the nut as opposed to the bolt. In a pinch, a grade 2 nut is sufficient for a Gr5 bolt and a gr5 nut for a gr8 bolt. Also, the washers look good with the stamp crowned side out, but they are stronger with the crowned side toward the workpiece -- The sharper edges of the flat side serve as stress risers, weakening the washer when that side bears tensile stress as it does when the bolt or nut bears on the crowned side.
larry

 

[SPYDERLK]

Every application for a washer that I can think of, right off, softer steel is good. When would you want washers to be grade-8 hard?

To stand up under the load and to spread the intense force applied by the bolt over a slightly greater area.
larry

 

[SPYDERLK]

I don't believe that bolt grade matters. The failure mode is in the bolt (shaft). Type of nut or threaded holes are irrelevant in terms of fastener failure.

I need to pick up some grade 2 bolts - where do I find them??

JayC

type of nut is important if its under tension a softer grd 2 or 5 nut will just have the threads pulled out of it once it gets near the breaking limit of the nut!

You can pick up a Gr2 bolt just about anywhere. Not a good idea to use them on your tractor tho. They stretch easily. Gr2 nuts can stand up ok to higher strength bolts once or twice, but I dont advise using them with a high strength bolt in a joint that is assembled and disassembled repeatedly unless you change the nut occasionaly.
larry