This standard describes the various classes of cold-water turbine meters in sizes 3/4 in. (20 mm) through 20 in. (500 mm) for water supply customer service, mainline metering, and custody transfer of water among purveyors, and the materials and workmanship employed in their fabrication. The turbine meters described in this standard are divided into class I and class II meters. Both classes of meters register by recording the revolutions of a turbine set in motion by the force of flowing water striking its blades. Class I meters are the vertical-shaft and low-velocity, horizontal-shaft models. Class II meters are the in-line, horizontal-axis, high-velocity-type turbines characterized by lower head loss and a wider normal operating flow range than Class I models. The major revisions to the standard in this edition include the following: reference to the discontinued ASTM D2135 has been removed from the references section (Section 2) and from the materials section for measuring turbines (Section 4.1.5); definitions for electronic display type and mechanical display type have been added (Section 3); UNS C89520 and UNS C89836 have been listed as acceptable materials in the materials section for meter and strainer main casings (Sec. 4.1.2); the flow rates in Table 1 for class II-type meters have been updated for the Safe Maximum Operating Capacity, the Maximum Rate for Continuous Duty, and the Normal Test Flow Limits (Table 1); and, the section on registers has been expanded to describe electronic display-type registers (Sec. 4.3.5 and subsections).