Guide To the Best Micrometers
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What Is a Micrometer?
A micrometer is a precision measuring instrument used by mechanical engineers, machinists and other workers in technical or laboratory settings. It measures length in microns, or thousandths of a millimeter.
Woodworkers seldom need as much accuracy as machinists. But they still use a micrometer for measuring dowel diameters, shim thicknesses and the depths of slots, holes and countersinks.
In its basic form, a micrometer is C-shaped with a fixed anvil on one end of the open C and a movable spindle on the other. You advance the spindle by rotating a thimble with threads precisely tooled to move it a fixed amount with every rotation. The measurement — the distance between the spindle and the anvil — may appear on a graduated scale on the spindle or display on a digital screen.
DIYers seldom need to measure with micrometer accuracy. A caliper — a ruler with sliding jaws — can perform many of the same measurements. A good set of calipers can measure with a tolerance of ± 0.001 inch. But plenty of measurements call for even more accuracy than that, such as:
- The diameters of thin wires;
- The diameter of an O-ring and the width of the groove it fits into;
- The depth of a slot in a workpiece;
- The thickness of a piece of sheet metal, paper or plastic sheeting;
- The thickness of the wall of a pipe or tube.
Types of micrometers
Different types of micrometers measure different things. The main types are:
- An outside micrometer, which measures thickness;
- An inside micrometer, which measures the inside diameter of a hollow object;
- A tube micrometer, which measures wall thickness of pipe or tubing;
- A depth micrometer, which measures the depth of a slot or hole.
Features to consider when buying a micrometer
- Resolution: Top-quality micrometers typically measure up to one inch, but those with lower resolution can measure up to six inches. If you don’t need the most accurate micrometer, choose one with a wider range and lower resolution. You’ll save money that way. For a woodworking project, you seldom need a tolerance better than 1/64-inch, which is roughly 0.4 millimeters or 400 microns.
- Digital vs. analog: There’s also a wide price difference between digital micrometers and less accurate, less expensive analog models. Although a digital display is easier to read, it comes at a premium you probably don’t need unless you’re doing precision machine work.
- Tip options: The tips of the anvil and spindle vary in shape.
- Flat tips are the most common. If you’re looking for a general-purpose measuring tool, these are the ones you need.
- Screw thread tips fit between screw threads, measuring their depth.
- Ball tips contact an object at a single point and are best for measuring round objects.
- Disk tips fit inside small spaces and are best for measuring inside diameters.
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Best Standard (AKA Outside) Micrometer
The Starett T444 Outside Micrometer comes from a company that has been making micrometers since 1880. It’s an analog model with a range from one to two inches, graduated in 0.0001 inch (2.54 microns) intervals.
This tool has a flat anvil and spindle, a knurled thimble grip for delicate measurements and a tapered head for taking precise outside diameter measurements in tight places. The carbide coating on the measuring faces resists wear and corrosion, making this a tool that will last.
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