Rules, scales, and length gauges are flat, graduated scales used for length measurement. Rules generally provide an approximate measurement compared to precision gauges. However, digital or electronic linear scales designed for OEM machine tool applications provide a high degree of accuracy.

Types of Devices

Rules, scales, and length gauges all measure length but differ in their composition, features, and suitable applications.

• Rules are tapes with a steel blade end and a straightedge which may or may not fold. This type of measuring tool is useful for those who take short measurements on a consistent basis. Flexible rules are made of thinner gage steel, plastic, or fiberglass. Specialized rules include the pocket rule for very small measurements and the circumferential rule for finding sphere diameters without calculation.
• Linear scales are electronic measuring instruments or rules with digital or remote displays for integration into OEM products such as machine tools, microscopes, precision tables or stages, and optical comparators. Various technologies are used, such as a mechanical rack and pinion, magnetic pickup sensors, and glass scales with linear encoders.
• Length gauges are measuring devices used to find the length to a surface from a fixed point. It implements a retractable rod and sensitive contact tip. They are used in product inspection, dimension checking during production, quality assurance measurements, and other industrial applications.

Important Selection Properties

When selecting rules, scales, or length gauges, the user must consider the application for which the device is being used. For frequent and general measurements, rules may be most suitable. Scales should be used where a higher degree of accuracy is needed along with the functionality of rules. Length gauges are for more detail rigorous applications where highly specified and accurate measurements are the highest priority over ease of use.

Specifications can be selected through the GlobalSpec SpecSearch Database Filter regarding a measuring tool’s units, graduation, length, material composition, and various features such as calibration certification that may be important.