On Wed, 19 Apr 2017 18:23:53 -0400, wrote:

On Wed, 19 Apr 2017 18:43:02 +0700, John B Slocomb
wrote:


Metric thread pitch is described totally different than inch size
bolts. Inch size is threads per inch. Metric thread is thread pitch -
so in inch size bolts, a higher number is a finer thread - in metric a
higher number is a coarser thread. A 6X10 metric bolt is 6mm with a
thread pitch of 1mm crest to crest (or root to root - however you want
to measure it)

Who cares, along as the people involved know what you are talking
about? Ant metering system is just that, a system which works for
those that use it.

The old method of measuring gear ratios on a bicycle was to use "gear
inches" which described the diameter of a wheel that would move the
distance in one revolution. Rather archaic today but made perfect
sense to those that used it.


As far as the "grade" of the bolt - a "grade 8" is NOT always better
than a "grade 5" or even, possibly, in some cases, a "grade 2"

A grade 2 or grade 5 bolt may bend and stretch - and still hold, where
a grade 8 would simply snap. It depends on what kind of load is being
carried by the bolt - and how it is torqued. On the same vein, a bolt
that is undertorqued CAN fail faster than one that is overtorqued. A
properly tensioned bolt is "pre-stretched" just enough that any cyclic
load does not stretch the bolt any farther, so the bolt does not
fatigue in use.

An exciting theory and technically correct. although I would comment
that I've yet to see an under torque bolt break.

It's far from "theory" - I've seen numerous head bolts and manifold
bolts fail that were attributed to being under-torqued on vehicles
that were not properly PDId, and quite a few bolts that failed in
shear because they were not properly tightened, and/or the holes were
not properly de-burred, allowing the bolt to loose tension.
No use arguing with Slocumb though - you'll never get anything
through his thick skull.

You must have a tremendous amount of experience with nuts and bolts.
As I mentioned I've been fooling with them things for about 70 years
now and frankly I've never seen "numerous" head bolts fail. Yes, I've
seen head bolts fail, but I would use the term "rarely" not
"Numerous". I would have to say that if you have seen numerous head
bolts fail then you are associating with some very incompetent
mechanics.

And how does one determine that they were under torqued after they
have failed?