If you're going to
have only one precision measuring tool Vernier calipers are the
best choice. I started out with an analog version and a few
years ago upgraded to this digital version. The analog
caliper had a max capability of 6 inches and at times that was not
enough, so the digital ones are 8 inch. So far I like this
range for the types of things I do. I have these within arms
reach of where I'm sitting now. The thing that makes
these so versatile is the three measurement modes:
- Making an outside measurement using the jaws as shown above
where a 60 mil minimum gauge pin is being measured
- Making an inside measurement using the points opposite the
- Making a depth measurement using the rod on the right.
To take full advantage of the above three measurement modes you
can use the yellow zero button when the jaws are not closed.
For example to measure the size of a step you could set the depth
rod on the first step and zero then put the rod on the second step
and read the difference between the two steps.
It's easy to forget that you
have changed the zero. If you do forget then the next
regular measurement will be WRONG. My rule is that if I
use the zero button as part of making a measurement I
immediately reset zero with the jaws closed before putting
down the calipers.
If the rod is too big to fit into a hole you can use a metal pin
and measure with the jaws, this time setting zero at the bottom of
the hole and reading with the pin out of the hole.
Harbor Freight 47260
made in China. The made in Japan calipers are better in that when
you turn them off the battery lasts longer. The made in
China calipers only turn off the LCD so the battery does not last
long. You can take the 357/303 battery (+ up) out when
you're not using them, but it's a PITA.
There are some weak points:
- When measuring thin items like a sheet of paper, the
thickness of a hair from your head, the thickness of a clock
suspension spring the half mil resolution is too coarse a
measurement. A micrometer (see below) is better for this
type of measurement.
- When measuring the inside diameter of a small hole the flats
on the inside measuring jaws do not allow them to seat on the
diameter but instead cause the reading to be a little
smaller. You could work up an equation based on the
known flat dimensions that would correct for this, but it
still would be questionable. A better way is to use plug
gauges (see below) to see which goes into the hole and which
is a no go.
This mike reads
to 0.000,05" i.e. 50 millionth's of an inch. Most 0-1" mikes
only read to 0.001 or a thousandth of an inch, but then there's
not much point in getting one if your calipers can make the same
In the photo at left the mike is showing 0.05950" where the right
most digit is either 0 or 5.
The problem with calipers is than when measuring things that are
thin you can't get much accuracy.
Also in the photo above is a set of 50 gauge pins from 0.011
to 0.060" in 0.001" steps all on the minus side of nominal.
Hopefully they will fill another weakness of the Vernier Calipers
and that's measuring the inside diameter of small holes. The
problem with the calipers is that the flat on the tips are a
little under 0.020" so when measuring a small hole they report the
I.D. a little smaller than it really is. Using pins should
me much more accurate for small holes.
The third item in the photo is a mike stand. I got three
different models to see which one I liked the best. The one
shown is the heaviest at 3 lb 20 oz and has about as small a foot
print of any of the others. For measuring small items that
can be brought to the mike the stand sure is great. Of
course the mike can easily be removed to measure things not
easily brought to the stand.
Let me know
about the cable needed
for remote readout.
9 March 2008- replaced the LR44 battery in the mike. Also
known as AG13. 1.55 Volts 11.5 mm diameter 5.65mm hi.
Positive toward cap.
.061 to .250 Plus
This pin gauge set is a continuation of the smaller set. The
box is 11" x 7½" x 2½" compared to the 4" x 3" x 2" for the
The mike is holding a pin reading 0.08010 which is inserted into
the solder cup of a 5590BA
Battery Adapter socket. This is the diameter that determines
what wire size will fit. Without this pin gauge set it could
not be measured accurately. I tried using two pins from the
smaller set and the answer was an ID that was too small.
* measure the ID of a solder cut
* measure the ID of shrink tube
* measure the hole where the high current output screw fits on the
EL1132 Electronic Load. Note the Screw Chek'R will not
accept the screw in 10-32 but it's very loose in 12-32. The
OD says it's a #10. The mating hole accepts a pin that's the
size of a 10-32 tap drill
the screw is a 10-32 but a little on the big side.
The mike has blue plastic plates on both sides where your thumb
and finger are going to hold it. That's to keep body heat
from expanding the metal. So another advantage of the stand
is you are not heating the mike at all.
There's probably some application where this stand might work
better than the one above. This would be my second
choice. All these stands to not hold the mike in a rigid
manner, but instead allow it to tip about an axis. This one
weights 2 lb 5 oz and is a little larger.
This stand would be handy for fitting into a tool chest or where
small size is important. It folds flat when not in
use. When the knob is tightened it not only clamps the mike
but also snugs the rotation about the axle. Has a couple of
coil springs to open the jaws.
123 Block (aka 1-2-3 Block)
These are hardened steel blocks with
outside dimensions of exactly 1 by 2 by 3 inches. These
came as a set of two. There are also 246 blocks that are
twice as big. The mike is reading 1.00000".
On the 2x3" face there are 5 tapped holes , the center and from
center the 4 diagonals, like 5 on a pair of dice. The
other 10 holes are 0.36" through.
The five tapped holes are 3/8-16 and in most the threads are
continuous all the way through. There are some web pages
that mention a problem with the threads in these holes, but mine
are fine. It's not clear to me how you can use the tapped
holes to join two blocks. Note the major diameter of a
3/8-16 bolt is about 0.37" and so will not go through a 0.36"
dia hole. The thing to have would be some pieces of round
stock about 1/2" long and a little under 0.36" diameter with a
hole drilled and tapped at the center of the length at 90
decreed to the center line for ¼-20 thread. This would
allow using ¼-20 bolts and washeers to make a 90 degree combined
123 fixture that was square.
Note on the left side of the micrometer frame just below the
mike barbell there is a blue plastic cap. When the cap is
removed there are 4 contacts on a printed circuit board for some
If you know what cable and connector work here let me know
When trying to figure out a way to measure the flywheel from a Toy Engine
using a pair of 123
blocks sure made it easy. The digital calipers are making
a deepth measurement from the top of the boss to the back plane
of the flywheel. Other measurements can be made to the
plane of the 3 bumps in a similar fashion.
I can see you really do want two blocks.
There are a number of
uses for the dial gauge. Mine is a Harbor Freight 623
sale item with the 5646
Magnetic Base. There are also much better analog and digital
Poor Man's Optical Comparator
When a flat bed scanner images an
object sitting on the glass and the file format is .bmp (and
maybe some others) the image retains size information. A
.tif file, like used in cameras is not a lossy format (like
.jpg), but it does not contain size information. So by
using a high resolution setting like 600 DPI or higher when you
work with the image in Photoshop or other image editing software
you can make measurements on the image which on the screen is
many times larger than life size. For example when looking
at some super flex wire the diameter of the striped end just as
it leaves the insulation is about 0.077 but toward the end where
it's been handled it's more like 0.113" across. This has
implications in regard to which terminal to use. I'm using
the HP 6200
flat bed scanner and
on WIN XP it works great (much better than the newer models).
Most threads are of the type made
by a "V" shaped cutter. There are threads that have square
walls and other specialized types, but the "V" type is very
common. The two key measurements are the pitch diameter
and the distance between adjacent threads usually expressed as
Threads Per Inch (TPI).
||An easy way to measure
the TPI is with a thread gauge. By holding the
gauge to the thread with a light background you can be
certain of the pitch. Sometimes at first glance a
thread appears to match, but when you rock the gauge the
section that matches moves back and forth that indicates
the thread is slightly different for the gauge
pitch. Instead of the gauge you can also use a
screw. So it's very handy to have a small
collection of screws and nuts in the more common sizes
handy for use a measurement tools.
|This is a metic thread
pitch gauge with 28 leafs.
||Another way to measure
the pitch is to use a flat bed scanner. When the
imaging format is Bit Map (.bmp) the image contains
scale information. That's not the case for Tagged
Image Format (.tif) or Joint Picture Group (.jpg) files
like used in a camera where scale has no meaning. The
pitch of the 4-40 brass screw shown in the photo can
easily be measured by using the ruler tool in a photo
processing software package like Photoshop. The
screw is from a Veeder
A nut is not a good way to determine pitch because when the fit
is sloppy you really don't know what's going on.
The best way to measure an outside thread is by using a pair of
ring gauges. One has it's internal thread set for the
upper spec limit for the class of thread, the "GO" gauge, and
the other is set at the minimum spec limit, the "NO GO" gauge.
way an internal thread can be tested with a GO - NO GO plug
gauge. The photo shows aGO NOGO plug gauge testing the
threads in a SDU-5/E Distress Marker
. These were made in high volume and as the
production taps wore out the threads got to be undersize.
Running the tap shown above cleans out the threads and brings
them into spec allowing my 5BA
to fit properly. The green paper is
the calibration certificate for the gauge.
A good way to check the pitch diameter is using plug or ring GO
For most cases measuring what's called the major diameter of a
screw or the minor diameter of an internal thread (pin gauges
are good for this) would seem to allow you to look up the thread
using a thread table (Google is helpful here). But that's
not the key dimension, the pitch diameter is what's
important. If the points are cut off a screw thread a
little more than normal the pitch diameter is not effected and
the thread may be fine.
Method of Wires
For measuring the pitch diameter of plug gauges or external
threads like a screw the method of wires can be used.
Three wires, all the same size, chosen so that the pins rest
very near the pitch diameter on the flanks of the "V". Two
pins on one side and one pin on the other side. Then a
mike held in a stand can be used to measure the distance across
the pins. From this can be calculated the pitch diameter
of the thread. This is the metrology standard method of
measuring pitch diameter.
The best way
to measure the pitch diameter is by using the method of
wires. Placing two wires on one side and a single wire on
the opposite side of a thread allows miking the diameter over
the wires. By choosing the diameter of the wires they end
up sitting on the flanks of the thread hopfully near the pitch
diameter. If the crest and root have had the points cut
off the wires will still measure the pitch diameter. This
is THE way to measure thread pitch and is the way plug gauges
to 48 TPI (0.5 to 6 mm) Pitch Thread Wire Measuring Set.
These also show up on eBay.
Using two wires on the left and one on the right to measure the
metric pitch dia on a UltraFire C3 flashlight
It takes one hand to hold the left two wires, another hand to
hold the flashlight body, another hand to hold the right wire,
and yet another hand to tighten the mike.
This is a 0.75 mm pitch so the 0,018" wires are used.
The two measurements (the ends are different).
Pitch = Measured over wires - CONST.
Using a hole template is not such a good way to make a
measurement, but is good for a quick sanity check. I have
marked the holes in this one for #4, #6 and #8 screws.
This is not too useful.
This is a way
to check the number size and the thread pitch. The
numbered holes to the left have no threads and are for checking
the O.D. and to the right are tapped holes to check the
pitch. A handy tool.
The Inch version is shown, but there is also a Metric
version. The Inch version has 28 and the Metric
version 21 tapped holes.
Using both the Inch and Metric size Screw Chek'R plates for the
screws from a Bunnell Telegraph sounder there are some screws
that can't be catagorized, either because the threads are rusty
or were made before there were good thread specifications.
This is where the leaf type pitch gauge comes in.
The leaf type gauge clearly tells you the pitch.
For these unknown screws a test of the mating part using a
modern screw is needed prior to chasing. Now knowing the
number size and pitch, the thread can be chased with a die.
Screw Gauge, F.E. Holladay, Dec 27, 1955, 33/199R
33/555.2 - applies to both the Inch and Metric versions.
Tap Handle & Die Holder
small taps have a square end that are 0.150" and the small tap
holder works with them. Small dies are 1" across the flats
hexagons and the small die holder is made to hold them.
They both, along with a number of taps and dies, fit into a
7"x7" Zip-Loc bag. I buy them on an as needed basis.
If a tap drill is needed it gets put in the bag too, not with
the regular drills. The store hanging card packaging is
also in the bag as a handy reference to coordinate drill size to
Most of the above measurements can
be done in either Imperial or Metric units. The digital
calipers and mikes have a button to change between the two
systems. But it's easy to calculate one from the
other. There are some places where it's not so easy.
The Go-NoGo gauges for example only work on the thread they're
made for. The lead screws in manually controlled machine
tools are either metric or Imperial. For an automated
machine it's less of an issue.
When measuring an unknown thread there's some chance that it's in
the other system. It's a simple matter to convert to the
other units and look up (Google) the possible screw sizes in the
There are two common ways of
weighing something. The balance is a lever arm where known
weights are moved on a beam to balance the unknown item.
These are common in doctor's offices. Scales use the
deflection of a spring. These are common in home
bathrooms. Balances give the same answer independent of
gravity, but scales read differently depending on the local
gravity. Gravity is far from constant and changes with
latitude. A change in gravity causes a scale factor change,
not a zero change. So to get really accurate answers from a
spring scale it needs to be calibrated using a known mass.