Metric Fastener System

[vtcnc]

OK, hopefully this doesn't devolve into a small civil war...

I've heard the pros and cons of Imperial vs. Metric unit systems. Quite frankly, I think if I was born into the Metric system, I would probably feel the same way about that as I do about our system of fractional measures here in the USA and other western societies...BUT I DIGRESS...dang, that was fast!

I have heard that the Metric Fasteners are an inferior design system- worse than the NC and NF thread systems. My question is why? What makes the NC and NF thread system better than metric threads? I'm really interested in the design and mathematic elements of the debate, because I feel that must be where the criticism takes root, this can't just be a national appendage measuring contest, right??

A thread is a thread, or am I wrong?? Or is it in the tooling? Is there something inherent in the proportions of a base 10 system that doesn't quite work right with cutting metric thread geometries? Do fractional imperial systems somehow lend themselves to being better fasteners? Why?

EDIT: after reading the first reply, I've edited my assumption after thinking about...what I have heard is that the Metric Fasteners are an inferior system, rather than design. So, I'm wondering if a person's dislike of the Metric System is just applied to Metric Fasteners just because it is inconvenient to work with two systems? No, what I have heard stated is that Metric Fasteners system is inferior to Imperial systems...I just don't hear compelling reasons why besides the Imperial vs. Metric argument.

 

[matthewsx]

I have never heard such a thing.

Quality fasteners are built to a specification which details their materials, strength, and use. I have seen metric fasteners labeled as 8.8 which are clearly not built to that spec but that's not the fault of the system, just an unscrupulous manufacturer.

Everything I know about fasteners is in this book which I highly recommend to anyone who wants to understand how these things work, AND fail....

www.CarrollSmith.com -- NUTS, BOLTS, FASTENERS, and PLUMBING HANDBOOK

Cheers,

John

 

[matthewsx]

I read all the Carroll Smith books when I started my racing kart business back in 2004. Especially like "Engineer to Win", he starts "with people noticed this red dirt got hard after being under a fire" and goes all the way through details on the strengths of modern alloy steel and non-ferrous metals. Good engineering info in a very easy to understand format.

Cheers,

John

 

[C-Bag]

I've never heard that metric is inferior either. The first 10yrs of wrench twisting was on air cooled VW's and took for granted the quality of the screws, nuts and bolts. When I went into imperial hardware it was confusing because of the odd sizes and grades but nothing significant. Not until I started acquiring Chinese made machines did I notice an actual quality difference. The hardware just didn't fit like the German hardware and it was pretty easy to find failures through corrosion or over torque. My impression is it has as much to do with cheaper alloys used as lax QC. Most of the hardware on my HF stuff is barely passable and if it's critical I usually replace it.

 

[higgite]

Wherever you heard that, did they say in what way metric threads are inferior to Imperial threads? Tensile strength, shear strength, taste, smell, social skills?

Tom

 

[Ulma Doctor]

i never thought of metric fasteners as being inferior to SAE/USS , just different.

i like metric better for smaller fasteners up to M6, but that is a personal preference rather than factual argument

i often drill out a stripped hole and replace the fastener with the next corresponding size, be it metric or USS/SAE

German made nuts and bolts are the best stuff out there, the DIN standards for fasteners are very high
Chinese made stuff, well- no so much

 

[C-Bag]

"i often drill out a stripped hole and replace the fastener with the next corresponding size, be it metric or USS/SAE "

ditto Doc. Whatever is in the junk bin and easiest to match up with a tap or die. I do rely a LOT on the junk bin of years of stripping off hardware of stuff that was going to get tossed. Metric and imperial, they do seem better quality than the stuff I get down at the hardware store. It's sad to judge a whole system by the present quality if you have no historical reference.

 

[Mitch Alsup]

None of the dimensions mater until you get to the point where rolled threads (head bolts, conrod bolts) are de rigueur. One can get bolts up into the 180K PSI range like 12-point NAS 627 bolts.

 

[darkzero]

i like metric better for smaller fasteners up to M6, but that is a personal preference rather than factual argument

I know nothing about the subject & haven't heard this either. I'm an imperial guy but I also prefer metric fasteners. No idea why that came to be though. I don't mind using imperial fasteners though, if I'm working on something that already has imperial fasteners then that is what I'll use & vise versa. I personally don't like to mix match fastener systems on a part, machine, vehicle, etc.

 

[royesses]

OK, hopefully this doesn't devolve into a small civil war...

I've heard the pros and cons of Imperial vs. Metric unit systems. Quite frankly, I think if I was born into the Metric system, I would probably feel the same way about that as I do about our system of fractional measures here in the USA and other western societies...BUT I DIGRESS...dang, that was fast!

I have heard that the Metric Fasteners are an inferior design system- worse than the NC and NF thread systems. My question is why? What makes the NC and NF thread system better than metric threads? I'm really interested in the design and mathematic elements of the debate, because I feel that must be where the criticism takes root, this can't just be a national appendage measuring contest, right??

A thread is a thread, or am I wrong?? Or is it in the tooling? Is there something inherent in the proportions of a base 10 system that doesn't quite work right with cutting metric thread geometries? Do fractional imperial systems somehow lend themselves to being better fasteners? Why?

EDIT: after reading the first reply, I've edited my assumption after thinking about...what I have heard is that the Metric Fasteners are an inferior system, rather than design. So, I'm wondering if a person's dislike of the Metric System is just applied to Metric Fasteners just because it is inconvenient to work with two systems? No, what I have heard stated is that Metric Fasteners system is inferior to Imperial systems...I just don't hear compelling reasons why besides the Imperial vs. Metric argument.

As posted by HM member EddyD, here is a pdf from the little machine shop on the the metric and imperial thread systems. It says that as imperial bolt size goes up one step it gives a 15% increase in strength. As metric goes up a step it only gives a 5% increase in strength.

Roy