Bob said:
> I want to be able to measure thread pitch and cut type in screws and bolts.
Large can of worms here:
In theory, any of the gauges are fine for pitch, though I can not speak to the
quality of those you linked and the quality can vary a LOT, both in pitch
correctness and finish, which will affect how well the gauge fits a matching
thread. I have several older gauge sets (mostly B&S triangular type) that are
great, and have needed to fix, or just canned, a couple more modern ones due to
poor quality. Don't count on them for form.
For form, the only really good option is magnification, so you can see if the
crests an roots are rounded, squareish, or sharp (Whitworth, US, metric modern,
or sharp), and even that is not sure, since wear and sloppy manufacture can make
it misleading. The best gauge is not economical: GO/NO GO gauges for qualifying
parts during/after manufacture. A toolmakers microscope, shadowgraph/optical
comparator, or decent digital microscope setup is ideal ($US1500 and up for the
toolmakers microscope, used, and similar for a used comparator barring luck,
maybe $100 to $200 for a bottom end digital 'microscope' that is good enough to
get detain and be low enough distortion that yuo can get the thread angle).
These can also do the duty of the thread pitch gauge, in many cases. I would
suggest a digital microscope, as it is useful for many other things, if the
money is available. I have all of them, and more, as I use these in part to make
my living, as do several others on the list.
Note that I have asked a number of times about threads I could not be sure of,
because measuring is only part of the job. Knowing the application helps a lot,
and information such as metric or imperial (some pitches and diameters are
mighty close) is key. The worst are where you have a mix of imperial and metric
involved, and the sizes and/or pitches are not standard to boot. It can be a
challenge. I have a number of references with outdated standards, and a lot of
data about specialty threads (Starrett, Stanley, B&S, Record, Lufkin, and so on)
and still run across things I can't ID.
****************
I would suggest that you get an imperial gauge with blades for up to at least
64TPI is you are looking at precision tools, where fiddly small screws ate
common (I actually have a gauge with blades to 120TPI I picked up from a watch
repair estate), but 48 TPI should be fine if your concern is primarily larger
tools (planes, &c) (for whatever reason, they often stop at 44, rather than 48,
but a 48TPI screw will work just fine as a gauge). You don't need every pitch to
be in the set. You can sight between pitches, as long as you are confident that
the thread is imperial.
For metric, there isn't a lot of issue, as the current pitch series is rarely
violated, but if you go back far enough, there are a few differences. Again, if
you go to the fiddly small (smaller than about 2mm), you will need either
special gauges (finer than 0.35mm) or magnification. I use a microscope at that
scale.
****************
In the grand scheme, the resource I most often use to identify threads is a set
of "Screw Chek'r" (Ruelle bros/Ruelle Industries) plates, and a kit I have
assembled of sample screws and nuts that I can use to compare, either directly
or under magnification.
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