[bullit4404]

I could probably do a ten part series on fasteners, types, plating, torque, uses, cutting threads, assembly, washers, thread lockers etc. But, I'm going to keep it simple. If you want to know more, look it up.
In the rest of the civilized world metric fasteners are used primarily and referred to as SI or System International.
In the US, metric fasteners are used as well as SAE or Society of Automotive Engineers.
When you buy a bolt, say an SAE 3 inch long bolt, 3/8" in diameter and UNC or UNF (coarse or fine thread), you would ask for a 3/8 UNC (16 threads per inch or TPI) x 3" long bolt. A metric bolt approximately the same would be M (metric) 10mm 1.0(1 thread per mm) X 75mm long. Make sure you get the right bolt and the correct pitch, ie # of threads per inch or mm. Your hardware guy should have a little "pitch gauge" to match you up. The head of the bolt will have either an M (metric) on top or slash marks (SAE) (see chart below) If you mix up M and SAE bolts, things will not go well for you. Never over torque your fastener. If you do, you may damage or break it.
Also, when you buy bolts they are graded ie grade 5 SAE or 8.8 metric. These are the strength ratings, how much you can torque them. There are torque charts for each size and type of thread. SAE go from 1-9, metric up to 10.9.
There are exceptions for special bolts. When you buy bolts, the nuts and washers must match by strength. That's right Bubba, you can't use a washer from your deck to back up your suspension bolts. As a rule, don't use lock washers. (They fail, like Skylights) Use a flat washer and a thread locker like Loctite.
Two technical terms to understand:
Tensile strength: If you pull on a bolt(stretch it) till it breaks you just tested the tensile strength.
Yield Strength: If you tighten a bolt until it starts to stretch (anything over .2% of length) you have reached the fastener's yield point. In some applications bolts are "torqued to yield" so that they act like a spring to hold something together. Aluminum cylinder heads on a cast iron block often use torque to yield cap screws (thread on one half of fastener) These are usually "one time " use only.
So match em up, torque em up, sleep well.

Thanks to Chuck for posting about impact guns, it reminded me to.....

 

[VIC-TIM]

great info!!!!

 

[pwd72s]

and remember...righty tighty, lefty loosey. Unless it's a reverse thread thing.

To get more serious...beware of counterfeit fasteners. I recall reading of defective rod bolts making it through the Porsche distribution channels. Turns out they were not made by the original fastener company, although all the labeling looked legit.

Now want to get really scared? Next time you're sitting on a runway, waiting for takeoff, remember that the article I read mentioned that counterfeit fasteners have been found within the airplane industry as well.

http://www.aia-aerospace.org/wp-content/uploads/2016/05/counterfeit-web11.pdf

 

[bullit4404]

I have a friend, who is a maintenance supervisor for an airline that operates out of Toronto. You don't want to know some of the stuff that goes on. His favourite line is: "As long as the AC and entertainment systems are working, we're good to go."
My friend Ross picked up his new Porsche in Germany. A Doctor picked up a new GT3 with a defective wiring harness. He made it 10 KM from the factory and it caught fire and burned to the ground.
He was given another one and the engine was replaced when he got back to Canada. (Rod bolts) I think they replaced several hundred engines.
There's a lot of off shore fasteners that are sub par. When in doubt go with the known, ARP, Paulin, etc.
Good input Paul!

 

[JackDW - 852]

Thanks for the info. I knew some of it but not a lot of the details you provided. When it comes to washers..... GUILTY

 

[Steve68Cougar]

The debate about lockwashers has gone on for a long time (since they were invented, most likely). I've worked for companies that use them all the time and I've worked for companies that insist they fail regularly. One of the companies I worked for ended up going from lockwashers to locknuts (mechanically deformed, not nylocks). The reasoning for that was as much to ensure that every bolt/nut combo was tightened with some sort of wrench and not just hand tightened. It's too easy to assemble something and just make it hand tight if you don't use locknuts. I've honestly only seen less than a handful of lockwashers fail. That being said, I'm not typically working with high stress, high vibration joints. The reason I mentioned deformed vs. nylocks is that nylocks are technically only good for one tightening. If it gets taken apart then you're supposed to toss them and get new ones. That rarely happens in the real world, though. Most of the time in non-critical situations they work just fine. As you said, much could be said about fasteners. People have devoted their entire lives to this topic (and facets of this topic).

 

[pwd72s]

And when you want those suckers to REALLY STAY PUT!

 

[bullit4404]

Have the tool, use it. Safety wire is good stuff.
Either that or Loctite red.

 

[bullit4404]

final repost