Specifies requirements for parallel screw threads having the Unified thread form for the diameter size range No. 0 (0.060 in) to 6 in inclusive. Limits of size for the Unified coarse, fine, extra fine, and constant pitch screws and a supplementary series of Unified threads of diameter greater than 6 in are given. It also covers screw gauges, associated check and setting gauges, and plug gauges with information being given on types of gauges, materials and hardness, general gauge design requirements, marking, and general notes on inspection of screw threads. Appendices give the basis of tabulated values, examples for calculating the limits of size of untabulated screw threads, notes on the production of external threads, notes on pitch and flank angle errors, notes on recommended system for gauging coated threads, and the limiting dimension of screw gauges for the more commonly used Unified threads.