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MEASURING THE THICKNESS OF METAL 109

is a soft metal, and if the sheet is thin enough, it can be cut with a pair of large scissors. It’s
easy to make hold- down straps and other parts using tin sheets designed for “punch” crafts.

Measuring the Thickness of Metal

There are many ways to denote the thickness of metal. The most common are:
• Fractional inch/millimeters. Metal primarily sold to consumers may be specified using
inches or metric units. Thickness is expressed in fractions, such as 3/64″ or 1/16″. When
in metric, the thickness is in millimeters.
• Decimal inch. There’s more precision in measuring thickness as a decimal value, down to
the thousandths of an inch. A thickness of .032 means the metal is 0.032″ thick— or
“thirty- two thousandths.”
• Mil. In this case “mil” doesn’t mean millimeters or millionths or military, but a unit of mea-
sure equal to one thousandth of an inch. A decimal thickness of 0.032″ is equivalent to
32 mils. By comparison, a plastic trash can liner is usually 2 to 4 mils.
• Gauge. This is a pseudo- standard used to specify the thickness of various materials, espe-
cially sheet metal and wire. Gauges of different types of materials aren’t always the same
(e.g., between plastic and metal), so you can’t readily compare one to another. Purely as
an example, 20- gauge aluminum is 0.032″ thick.
Complicating matters: When used with metal sheet, gauge varies depending on the
metal. That hunk of 20- gauge aluminum is equivalent to something between 21 and
22 gauge for steel, and 13 gauge for zinc.

You need a machinist’s micrometer (Figure 11-2) to accurately measure the thickness of metal.
Digital micrometers can be switched between decimal inch and other units of measure (typically
millimeters), but less expensive models just have a mechanical scale, which can take a bit of
G getting used to.
They’re not hard to operate, but you’ll want to read the instructions that come with the tool
for general guidelines on how to read the markings. When using micrometers marked in inches,
the measurement will be in thousandths of an inch, .001″. Most metric micrometers are marked
in half- a- millimeter steps.

"Jaws" Read major
size here
Spindle
Thimble
Drum
Figure 11-2 Use a micrometer to
Fine adjust
Add remainder measure the size or thickness of
shown here small parts.

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