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Measurements In Bullets, Wire And Nails
Can you explain the diameter measurements used
in bullets, wire and nails
All three of
these questions have to do with unusual units, and they all show just how
interesting measurement systems can be!
Bullets
Bullets come in
variety of different calibers. The caliber indicates the diameter
of the bullet. Some common calibers include:
·
.22
·
.25
·
.357
·
.38
·
.44
·
.45
For example,
you have probably heard of a ".22 caliber rifle."
In all of these
cases, the caliber number indicates the diameter of the bullet in inches.
So, a .25
caliber bullet is a quarter of an inch in diameter.
Words like
"Magnum" and "Special" imply that a higher-energy powder is
used with the bullet.
This page has a lot
of information on bullet calibers. It also talks about the gauge of shotgun
shells and says that the gauge numbers for a shotgun (12 gauge, 14 gauge, etc.)
are "the numbers of lead balls -- of diameters equal to the inside
diameter of the gun -- that are required to total up to a pound of lead."
That's about as weird as units get!
Wire
The
measurement system for wire is also interesting.
AWG stands
for "American Wire Gauge" and is a standard in the United States
for wire diameters.
In a house, you
typically find 10, 12 and 14 gauge wire, and electronics projects typically use
20 gauge wire.
Wire gauges run
from 000000 gauge, which is about half an inch in diameter, down to 40 gauge,
which is 0.001 inches (this page has
a complete chart). The higher the AWG number, the thinner the wire.
Where did this
odd system come from?
According to this page, "The
modern method of drawing wire is believed to have originated in Europe late in
the 13th cent.
In this process the metal is pulled, or drawn, through a number
of holes, each smaller than the one preceding, until finally it is passed
through the hole having the desired diameter."
The gauge
number stems from how many holes the wire is drawn through, and the more holes
it's drawn through the smaller the diameter.
This page has
some good information on wire resistance.
Nails
Then there is
the common penny designation used with nails. You can buy
nails ranging from two-penny to fifty-penny in the United States (represented
as 2d or 50d, respectively).
Why is
"d" used instead of "p"? According to this article,
"This stems from Roman times.
The
"d" stood for "denarius," a small coin common throughout
the Roman empire."
The penny
designation can be translated into length, as shown on this page.
It's not clear
that anyone knows where the penny designation comes from -- it might have
indicated the cost of 100 nails in the 1400s.
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