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.

I served a 4 year apprenticeship and had my papers as a journeyman
machinist in 1950. Was a licensed A&E mechanic two years later (note
in those days it was Aircraft and Engine) joined the Air Force to
avoid being drafted and was in aircraft maintenance for 20 years.

When I retired I went to work in the mining business where that called
me a "Master Mechanic" for some reason.

So yes, I reckon I do know a bit about fasteners, having dealt with
them for 70 years or so. Certainly not everything but probably enough
to tell the difference between a metric and inch thread.

Some are pretty difficult to differentiate between without having the
wrong bolt for the hole, or the wrong nut for the bolt/stud.