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.

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.

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.

These calipers come with a calibration certificate traceable to NIST that states they've passed a test for accuracy. Short, narrow contacts allow them to take hard-to-reach measurements, such as the dimensions of internal grooves and slots. All are IP67 rated for protection from dust and temporary water submersion. They have a zero-set button which allows you to start measuring at any point.

Short, narrow contacts allow these calipers to take hard-to-reach measurements, such as the dimensions of internal grooves and slots. They are IP67 rated for protection from dust and temporary water submersion. Each has a zero-set button which allows you to start measuring at any point.

Short, narrow contacts allow these calipers to take hard-to-reach measurements, such as the dimensions of internal grooves and slots.