Calipers typically use a precise slide movement for inside, outside, depth or step measurements. Specialized slide type calipers are available for center, depth and gear tooth measurement and gaging machine table travel. Some caliper types such as spring / fay or firm joint calipers do not usually have a graduated scale or display and are used for comparing or transferring dimensions.

Caliper Types

Common types of calipers include:

Center measuring- A center measuring caliper has conically pointed jaws designed to measure the distance between the centers of two holes.

Gear tooth- A gear tooth caliper has an adjustable tongue designed to measure the thickness of gear teeth at the pitch line. The adjustable tongue sets the measurement depth at the pitch line or addendum.

Machine travel- Machine travel calipers are designed to measure the travel or position changes of a machine bed, table, or stage. These gages are typically mounted on a machine or are built into a product including machine tools, microscopes, and other instruments requiring precision dimensional measurement or position control.

Nib jaws- Nib shaped jaws facilitate measurement of inside features (ID), outside features (OD), grooves, slots, keyways or notches. Compared to the blade edge typically found on standard calipers, the nib is more easily and accurately located on an edge or groove. Small, pocket-sized calipers are usually designed for low precision gaging applications.

Pocket or rolling mill- Rolling mill calipers are usually simple rugged devices for quick gaging of stock in production environments. 

Slide caliper- Sliding calipers use a precise slide movement for inside, outside, depth or step measurements. While calipers do not typically provide the precision of micrometers, they provide a versatile and broad range of measurement capability: inside (ID), outside (OD), depth, step, thickness and length. 

Spring or firm-joint- Spring, Fay, firm-joint or other radially opening type calipers have jaws that swing open with a scissor or plier-type action. These calipers are commonly found in non-graduated versions; although units with graduated, dial, or digital displays are available.

Display Options

The display on calipers can be non-graduated meaning that the caliper has no display, dial or analog display, digital display, column or bargraph display, remote display, graduated scale display, or Vernier scale display. 

Specifications

Important specifications for calipers include the range and the graduation or resolution.

• The range covers the total range of length or dimension that the caliper can measure.
• The graduation or resolution is the best or minimum graduations for scaled or dial-indicating instruments, or the best or minimum resolution for gages with digital displays.
• Measurement units for calipers can be either English or metric. Some calipers are configured to measure both.

Features

Common features of calipers include depth attachments or gages and marking capabilities.

A depth attachment is a gage specialized for depth measurements usually consisting of a solid base with a protruding rod or slide. The solid depth base provides a reference and support across the opening.

Marking capabilities include gages that accommodate a scribe or other device for accurately marking a component at a specific measurement along a particular dimension.

Standards

The American National Standards Institute (ANSI) specifies the standard ANSI Z540.3 to establish the technical requirements for the calibration of measuring and test equipment.

Resources

The Caliper: A Simple, Essential Tool Since Roman Times

Vernier Caliper

What You Must Know About Calipers

Image credit:

Mahr Federal Inc.