Most people get in the habit of thinking of bolts according to the hex head size, the socket or wrench needed to turn them. Consequently we say: "Oh yeah - that's a nine sixteenths!" (or a half, or a 14 or something)

But bolts are actually defined and described based on several very specific characteristics that we need to know in order to find a replacement - for one thing. Or to decide what to use in a new project. But we VERY DEFINITELY need to know the right terms in order to SEND FOR one from somewhere(!) And this is a technical lingo that is easy to pick up, but if you don't know the language you could well try to order a Pizza and end up with a bucket of Clams - so to speak. So we should explore this.

There are so many different styles and kinds of "HEADS" of bolts that to list them all would be complete overkill. Allen, Tamper Resistant, Hex, Twelve Point, Clutch, TORX and so on...

But a bolt is really defined by the diameter of it's shaft, the number of threads per inch (or per millimeter, in metric), the depth that the shaft reaches, and the tensile strength - based on what kind of material it is made of and any kind of heat treatment or tempering that is done to them.

As I tap away at this keyboard tonight, I am close to the end of a long shop re-organization project and have before me one last engine that I have to put on a stand. The "M" and "W" 351's I had laying around were no problem. I have a set of bolts on order for the last 351 I need to get up on a stand and the nomenclature for those bolts is: 7/16 -14 x 2 1/2 Grade Eight HEX which translates into 7/16 inch shaft diameter, 14 threads per inch, 2 1/2 inch depth of shaft as measured from the bottom of the head to the end of the bolt, Grade eight is a much higher strength bolt than mild steel, and of course: The head of the bolt is a common HEXAGON pattern.

But there is one more puzzle left: The 2.3L (Duramax?) engine that came out of my '89 Ranger...

I found one of the original bellhousing bolts, and it is definitely Metric, it measures about 10mm through the shaft, which makes it a metric M6 bolt. (M6 = 10mm diameter) What that is in SAE is about 25/64" or so... It falls between 25/64" and 13/32". Ten mike is about there

I am still not sure of the thread pattern though - I don't have a true metric thread gauge. But it seems to fall exactly between 14 threads per inch (TPI) and sixteen. I have seen references to this, a 15TPI M6 bolt - but that isn't the correct metric nomenclature. I'm not sure if that is an M6 -1.0 or an M6 -1.25 or what exactly.

To order a metric bolt we also have to know how long it needs to be. In this case it isn't going into a transmission bellhousing but into an engine stand mounting stand-off. They are usually about two inches, two and a half inches allows for the part that will thread into the block, and I can get that factor once I get the stand back to the shop tomorrow.

I don't know if I am alone in not quite being able to easily wrap my head around metric bolt sizes and thread patterns. The major difference is that instead of counting the turns over a full inch, metric bolts are in threads per millimeter - which is a very small measure.

14 threads per inch is considered fairly coarse in a 7/16ths bolt. I grew up hearing the terms "National Fine", "National Medium" and "National Coarse" (not to mention "PIPE THREAD") and I dunno if any of these terms have a parallel in metric standard.

So while my thoughts are still fresh on my recent 'Adventures in Hardware' I thought I should set them down for posterity and see if anyone else has some good clues, insights, or inspirations on this truly very basic topic...

CHEERS!
~Wolfie

 

I thought I should tell you that what we are talking over here could well, and I hope, become a featured article at FTZ. I did not trust my own knowledge all by itself, and that is why I chose to explore it all in a group format where all can contribute what they know so that we can put together the best and most complete information that we have.

AND everyone that contributes to the thing, will be given credit in the final form of it - the write up.

~Wolfie


PS: I think in the final write-up I see it as "Understanding BOLTS"

 

Just reading your post, A m6 bolt is not 10mm diameter. A m6 is 6mm diameter and a m10 is 10mm diameter. Maybe be a typo? And the pitch is distance between threads not number of threads .

 

Are you sure about that? Can you link a chart?

I do NOT want to be wrong about what I send for for the 2.3L

What I SAW from hardware companies was that M6 WAS ten mill diameter.

(We have our first misinformation point)

CAN YOU PROVE WHAT YOU SAY?

Show me a reference, and show me it right now!

Searches I did earlier today called out M6 as a ten. ~ You need to show me proof of otherwise.

 

Yes I am sure, I built machine tools that where all metric fasteners. A common hex m6 bolt would have a 10mm hex head.

 

Google metric bolts

 

I stand corrected (so far) because I found this link - which tends to support you:
http://www.fastenermart.com/understanding-metric-fasteners.html

YOU challenged me, you have stones son - what's your true name?

(I'm Dutch)


You may have saved me from wasting a wad of cash...


~ But the whole reason for this thread is to straighten all that stuff out...
YOU DID GOOD! Welcome to the ZONE!


~and before you ask, I put a "LIKE" on all of your posts in this thread - because you told me the truth


*There's a lot of confusion about "METRIC"

 

I am not trying to start a pissing match, I say something that I knew was wrong, thought it was just a typo. I have spent the last 35 years working with metric fasteners, So I said something. Sorry if I stepped on any toes.

 

You didn't hurt my toes, bro - I'm after the real deal here, and it seems like YOU HAVE GOT IT - so please clue the rest of us in. WE NEED that

Can you clarify that?

Threads per inch is simple, we just count them.

DISTANCE between threads sounds somehow like nuclear science...


*You got a wild lookin' truck, BTW

 

You can buy cheap thread pitch gauges.

 

I was hoping to find someone who understood it - and can explain it

You can buy a gauge, but not understand what it means

I don't know if that makes any sense - but that is what I am after

The explanation behind the gauge

 

I wonder why it is that when we discuss things we do not fully understand - it seems as if it must be a challenge, a hunt, an argument. When what it really is - it's a "SEEKING AFTER KNOWLEGE" that we all can share.

Peace, Brother. I only want to know what YOU know....

And I will share my own with you if you need it
***He statezzz, quietly***

 

good start wolf

 

The pitch is the distance between each thread. If you want to convert to threads per inch, First multiply the pitch by .03937 and then divide 1'' by that number. A 1.0 pitch would be 25.40 threads per inch. I hope that helps.

 

SAE is pretty easy for me, been around it all my life. Metric, that's a different story. With todays, vehicles, well, actually with the vehicles for over the past 30 years, knowing the differences between metric and SAE, how to order them when needed, etc is important. Not to get off topic, but why are so many vehicles built using both types of bolts?