This Standard specifies the geometry and method of use (installation and flowing conditions) for orifice plates, nozzles, and Venturi tubes when they are inserted in a conduit running full, to determine the rate of the fluid flowing. It also gives necessary information for calculating flow rate and its associated uncertainty. It applies only to pressure difference devices in which the flow remains turbulent and subsonic throughout the measuring section is steady or varies only slowly with time and the fluid is considered single-phased. In addition, the uncertainties are given in the appropriate sections of this Standard for each of these devices, within the pipe size and Reynolds number limits which are specified. It deals with devices for which sufficient calibrations have been made to enable the specification of coherent systems of application and to enable calculations to be made with certain predictable limits of uncertainty. The devices introduced into the pipe are called primary devices. The term primary device also includes the pressure taps and the associated upstream and downstream piping. All other instruments or devices required for the measurement or transmission of the differential pressures are known as secondary elements, and in combination are referred to as the secondary devices. This Standard covers the primary devices; secondary devices will be mentioned only occasionally. The following primary devices are covered in this Standard: (a) orifice plates, which can be used with the following arrangements of pressure taps: (1) flange pressure taps, (2) D and D/2 pressure taps, (3) corner pressure taps. (b) nozzles: (1) ASME long radius nozzles. (c) Venturi tubes: (1) classical Venturi tubes. This Standard does not pipe or conduit sizes under 50 mm {2 in.} nominal. This Standard does not apply to ASME Performance Test Code measurements. The Standard is applicable to measurement of flow of any fluid, (liquid, vapor, or gas).