Guide To the Best Micrometers
A micrometer can measure the thickness of a human hair. If you need this kind of accuracy, here are some of the best micrometers you can buy.
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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.
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.
Best Inside/Outside Micrometer
The Mitutoyo 146-131 Micrometer offers a unique spindle design with 1/4-in. disks. That allows it to measure outside diameter up to one inch, and inside diameter within 0.55 to 1.050 inches. It can also measure hole depth.
It features a satin chrome finish, knurled thimble grip and a ratchet stop on the end of the thimble that you can tighten to preserve a measurement for later reference.
Best Tube Micrometer
The Anytime Tools Tube Micrometer isn’t the most sophisticated tube micrometer out there. But it’s accurate enough for most DIY purposes, and it’s one of the most affordable. The anvil is positioned perpendicular to the spindle so it can fit inside a pipe or tube casing when measuring the wall thickness.
This analog micrometer has scale graduations in increments of 0.0001 inch (2.54 microns). It features a ball tip on the anvil, which compensates for the curve of the tubing by contacting it at a single point. That improves measurement accuracy.
Best Screw-Thread Micrometer
The Accusize Screw-Thread Micrometer measures between one and two inches with an accuracy of 0.00016 inch (0.004 mm). Accusize also makes models with larger ranges for larger screws with the same measurement accuracy,
The conical tips of the spindle and anvil fit inside the screw threads to measure their depth, This micrometer comes with a selection of tips for measuring threads of different widths (measured in threads per inch, or TPI). The tips are interchangeable to measure threads from 3-1/2- to 44 TPI.
Best Depth Micrometer
The Mitutoyo 129-132 Depth Micrometer comes with six interchangeable rods to measure depths up to six inches. The tool itself has a four-inch base that straddles the hole, and the rods are precisely calibrated in one-inch increments. Each rod has an accurately ground, flat carbide face.
The micrometer caliper is graduated to an accuracy of 0.001 inch (25.4 microns). The thimble comes with a ratchet stop so you can preserve measurements for later reference.
Best Budget Micrometer
The Anytime Tools 0-1 Inch Micrometer has the same 0.0001 inch (2.54 micron) accuracy as models that cost three times as much or more. It’s an outside micrometer with carbide anvils and a ratcheting thimble extension that advances the spindle slowly for more accurate measurements.
Anytime Tools also sells micrometers that measure from two to six inches. They’re all inexpensive, so if you need a collection for your workshop, you can buy several for about the same price as a single micrometer from some of the other manufacturers.
Best Budget Digital Micrometer
There’s no denying a digital readout improves accuracy and is easier to read, but you usually have to pay quite a bit more for it. Not so with the Vinca DMCA-0105 Outside Micrometer, which costs less than many analog models.
This micrometer is super precise, with a resolution of 0.00005 inch (about one micron). One big advantage: The digital display converts between metric and imperial units so you don’t have to.
Best Micrometer Set
If you need micrometers that measure in several ranges, you’re better off buying them in a set. The Wondersunm Six-Piece Outside Micrometer Set is an affordable and reliable choice.
Each of the six units (which come in a handy toolbox) measures in a different range, up to six inches in one-inch increments. Accuracy is 0.0001 inch (2.54 microns), and each unit features a ratcheting thimble stop for added accuracy.
Best Overall Micrometer
It has a ratchet stop and carbide-tipped anvil and spindle. But what sets this one apart is the IP65 ingress protection that prevents contamination from dust and water. This allows for an accuracy tolerance of ±0.00005 inch, better than most models offer.