Spring tension forces two telescoping steel contacts to expand inside the bore; turn the screw to lock the contacts. To find the bore diameter, use a micrometer to measure the distance across the contacts.

Check a variety of hole, groove, and slot diameters. Each gauge in these sets has a different measuring range. The end of these gauges has a 360° contact surface that’s easier to center in tight spaces than anvils or spring-loaded contacts. Use them to measure slots and bores in precision parts, such as electronics, where small size deviations can cause inefficiencies.

Insert the probe into a bore and turn the knob on the handle to expand the contacts. To find the bore diameter, use a micrometer to measure the distance across the contacts.

Full-ball gauges are best for deep bores. They’re less likely than half-ball gauges to tilt within the bore, which helps to avoid skewed measurements caused by placing the gauge off-center.

Half-ball gauges are best for measuring near the bottom of flat, shallow bores.

Measure the diameter of small holes, grooves, and recesses. These gauges help you find deviations in size or roundness that can cause precision parts, such as engine or valve cylinders, to wear quickly or run poorly. They have a full-ball probe, which has a 360° contact surface that’s easy to center in tight spaces. Compared to gauges with an anvil, spring-loaded contact, or half-ball probe, they’re less likely to tilt inside a bore and skew measurements.

Insert the probe into a bore and turn the knob on the handle to expand the contacts. Measure the distance across the contacts with a micrometer to find the bore diameter.

Measure the inside diameter of holes and cylindrical bores, as well as identify out-of-roundness problems. Switch between anvils to measure holes of different diameters. They have highly sensitive, wear-resistant jeweled bearings for a long service life.

Use these bore gauges to measure the inside diameter of holes and cylindrical bores, as well as identify out-of-roundness problems. Since they measure in increments of 0.0005", they’re useful for general checks. They’re often used to test parts where deviations in roundness or size can lead to wear or inefficiency, such as in engine cylinders, machine components, and turbines. Unlike calipers and inside micrometers, these bore gauges have a long shaft to reach into deep cylinders. They have a two-point contact system, which is the most common design for bore gauges.

To use these bore gauges, set a baseline measurement with a ring gauge, calibrator, micrometer, or caliper. The variation from the set measurement displays on the dial right away, so there’s no need for conversions. Swap out the anvil to measure bores of different diameters. All these gauges have jeweled bearings that resist wear for a long service life.

For technical drawings and 3-D models, click on a part number.

Set includes one dial head that fits onto three gauge bodies. Use these to measure the inside diameter of holes and cylindrical bores, as well as identify out-of-roundness problems. Switch between anvils to measure holes of different diameters. The dial head has highly sensitive, wear-resistant jeweled bearings for a long service life.

Find the inside diameter of cylinders and rings. These micrometers have a plain thimble, which relies on operator feel for accurate measurements.

124 series have solid steel extensions that attach at one end of the micrometer head.

823 series have lightweight tubular extensions that can attach at either end of the micrometer head.

Collars (sold separately) extend a micrometer’s measuring range. Handles (sold separately) screw into a micrometer head to extends its reach for measuring deep holes.

The jaws on these micrometers work like caliper jaws to precisely measure inner diameters. These micrometers have a friction thimble with a constant-force mechanism, so they stop tightening once both jaws touch the sides for repeatable measurements. When the jaws stop tightening, the thimble continues turning with resistance, preventing overtightening. Use the included setting ring to calibrate and verify the accuracy of these micrometers.

Micrometers with pointed tips help you measure small shapes on your workpiece. Their thin tips fit into recesses and grooves, such as those found in keyways.

Micrometers with anvil tips are used to take quick ID measurements. A wide surface keeps the tips from catching on ridges or bumps, so it’s easy to position them across the diameter of your workpiece.

Measure the inside diameter of cylinders and rings. These micrometers have a plain thimble that turns freely without friction or a stopping device. It relies on user feel for accurate measurements. All include steel extensions that you can attach to one end of the micrometer head.

With an LCD screen, these micrometers make it easy to read inside diameter measurements taken from cylinders and rings. Place the micrometer inside your bore, then turn the thimble until the spindle makes contact with both sides. For an accurate reading, stop turning as soon as you feel resistance on the thimble.

USB data cables (sold separately) connect micrometers directly to your PC.

10-pin data cables (sold separately) connect micrometers to a Mitutoyo miniprocessor or multiplexer.

Wireless data transmitters and receivers (sold separately) let you send data from micrometers to your PC without a cable.