"Basics of Basics" Nuts and bolts
“Basics of Basics” Nuts and Bolts.
(Yes we are talking nuts and bolts that hold your car together.)
By Brian Martin
Today at work I was again reminded that not all of us have a basic understanding in nuts and bolts. I was asked to get a “10” bolt. (insert rolling eyes smilie) What the guy was referring to is a bolt that used a 10mm wrench on it. That my friends is not how you measure a bolt. A bolt is measured by the diameter and length of the threaded area. And again, there is the thread count making it “fine” or “course” thread.
This is the basics right? Well, that is it, diameter, length and thread count. With those three things you can call up a store and order the right bolt over the phone. You can’t if you say “10” as your size.
The “head” of the bolt will determine the size wrench you put on it. That doesn’t mean for a second that the diameter of that bolt is going to be a given diameter. You can find ¼” bolts with 7/16” heads on them as well as 5/16” bolts with 7/16” heads on them. Just as on a late model car you will find 6mm “shanks” (the threaded area) with 10mm heads (the most common bolts found on a Japanese car body) to 8mm shank bolts with a 10mm head (commonly used on the door check straps).
Then we have “types” of bolts, you have button head allen “cap”, you have hex bolts, hex with a little washer built in, there are lot of different styles of bolts.
Here is a little chart showing the different types. http://www.boltdepot.com/Fastener-In...ype-Chart.aspx
This being the “basics”, honestly you only have to know the few that are on your car. Most likely hex holts both with our without a built in washer and a couple of different trim screws with or with out an oval head or pan head, that is about it. 99% of the average car is going to be limited to those four fasteners.
And yep, there are plenty of cars out there with torx and a couple of others with more and more late model cars using these. But for most older cars the four mentioned are going to cover you.
Torx is called not by a measurement but a “size’ T15, T25, etc.
The Torx is a star shaped hole in the head of the bolt. There are also male torx bolts which is just the opposite.
The head of the Hex bolt is measured like this, this one being 9/16 inch across, thus a 9/16” wrench is used. If it were metric it would be in millimeters 10,12,14 are common.
This is where the shank is measured to determine the diameter.
Again, with a metic bolt, it will be in millimeters 4,6,8, and an SAE bolt in inches ¼”, 7/16”, 5/16” etc. This one being 3/8”
The thread count is measured by a neat little tool (tread gauge), this one being metric. The metric bolts threads are measured by the distance between threads in a millimeter. So you will commonly see 1.25 and 1.50.
The SAE bolt is measured the exact same way, only in inches. It is measured by the amount of threads per inch. 18, 24, 28 threads per inch are common.
Don’t take for granted that you are going to have “fine and coarse” threads and that is it, there are many found that are not a common thread. We had one the other day at work where a bolt was needed for the handle on a spray booth and it ended up being a ¼” bolt with 24 threads per inch, very uncommon and we didn’t have one in the shop to replace it. Some will even say this size doesn’t exist, that it is a metric 10x1.0 but that thread gauge didn’t work on it and I found 1/4x24 nuts and bolts on the net, so yes they do exist.
The point being, if we would have assumed it was a “fine thread” ¼” and ran one into it, we would have ruined the threads.
These measurements are for commonly found SAE and metric bolts in America. There are other types of bolts using different thread “Pitch” measurements around the world.
As for “grades” or “strengths” in metric the higher the number the “harder” the bolt. And in SAE, the more “bars” on the top the harder the bolt. Notice I didn’t say “stronger”, because “hard” doesn’t mean strong, it only means hard. There are a lot of cases where a harder bolt would break because of the forces on it than a softer bolt.
Basically, around the cars body which is what I am most familiar, very low grade is all that is needed, I don’t care if it is a hinge or a fender, it is going to be strong enough. While when you start talking engines and drive lines, I suggest you do your homework before you grab a bolt at the hardware store for your four bar link.
Brian, I hope its okay to add something to this.
There's a common school of thought that stronger is always better. There's probably no area where that's more prevalent than in bolt selection.
But, I recently read an article in one of the trade magazines which said the SAE (Society of Automotive Engineers) has recently issued a statement advising against the use of metric 12.9 grade (the strongest commonly available metric grade) in any automotive application unless the strength of the 12.9 is an absolute necessity as proven by engineering studies.
This was prompted by all the big 3 manufacturers having experienced breakage of 12.9's which were used in applications where 10.9's were adequate, but the designer chose to spec 12.9 just for what he assumed would be a bit of extra insurance.
The article was just a fairly short blurb that didn't get into the details, but it would be a safe assumption if a stronger bolt is breaking where a weaker one wouldn't, then the particular joint needs the additional elasticity of the slightly weaker bolt in order to survive.
Anyway, I figured this is worth posting for anyone who's working on something with metric fasteners. The 10.9's, which are the closest equivalent to an imperial grade 8, would be most likely to be found in suspension attachments and such, so something the owner might assume to be an upgrade, like putting everything back together with 12.9's to replace the 10.9's, could in reality create a more dangerous situation rather than a safer one.
Don't forget to add it to the Crankshaft Coalition Wiki compilation, if it's not already there.
sometimes harder is NOT better,,the harder they are,, they are also more brittle..making them prone to snap instead of give ,or flex.. this would make them a safety issue and certainly a big issue on suspension or any other parts that you would bet your life on...bolts snapping ,,suspension falling out at 100 m.p.h. would ruin your day ,,if not your life..
grade 3- too soft 5-8- best gr.12-too much ...
.....at least that's the way i understand it....
I agree, so i recommend to use the ones especially designed for a specific purpose, studies does show that 12.9 grades are more brittle than the lesser grades. Learned this when i installed a 12.9 in replacement of my 10.9 Mr Gasket Bolt.
can i just add that the correct torque is very important as most people think tighter is better but they are wrong invest in a good torque wrench
Nice job, Brian. You really ought to look into compiling these articles you write and publishing them. Kind of like an automotive guide for beginning enthusiasts. Cool stuff and well written. :thumbup: Dan
I think a link or a copy and paste of what they need is better than a link to a website selling a book. :)
A few years back I got a catlog from Coast Fabrication, a supplier of fasteners for race car applications amongst other things. Their catalog contains a lot of technical info on fasteners and I use it as a reference for just about any fastener issue. Most all of that info is also available on their website.
They too make a comment about what grade of bolt is better suited in specific applications. One such comment is that AN series bolts (essentially equivalent to Grade 5 hardware) is ' Vastly superior to Grade 8 tension bolts for nearly all shear-type, race car applications'. This simple statement wades into the significant concept of proper fasteners for joints held in tension and those held in shear, something that is (or should be) well-analyzed by the engineer designing the application.
Regular everyday "bolts" are usually referred to in hardware catalogs as "cap screws"
There are also "machine screws" that have slotted, phillips, (or here in Canada ... "Robertson" square hole socket heads.)
#6 to #14 sizes are common, with various thread pitches depending on diameter (eg. 10-24, 10-32 TPI)
#12 = 3/16"
#14 = 1/4"
So perhaps Brian's 1/4" - 24 could have easily been a fine thread "machine screw" as opposed to a "cap screw"?
There are "standards" when it comes to fasteners. The ASME (American Society of Mechanical Engineers) provides one set of standards ... but I recall reading somewhere that fastener specs may be in a state of transition ... or that there may be a somewhat paralell standard in place, depending on geography?
Grade 5 bolts are definitly less brittle than a grade 8 ... I've seen the difference in action.
Lots of farmers will use a (for example) 3/4" x 4" bolt as an improvised hitch pin. (Not that I'm advocating this practice ... just an observation.) :D
Yup, they will get fairly contorted - looking but seldom seem to shear off.
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