Describes the characteristics of three sizes of reels for 12.7mm wide magnetic tape to allow physical interchangeability. Their dimensions differ only in the overall diameter of their flanges. All other requirements apply equally to all three sizes. Intended for applications where the larger reel is not used. Cannot be used with the self-loading cartridge. Covers references, conformance, description, dimensions, other physical characteristics, identification of ownership, and manufacturer's reel identification.