5/16-24 NF GH3 USA

5/16-24 NF GH3 tap. The "5/16-24" indicates the size and thread pitch, where 5/16 is the nominal diameter in inches, and 24 is the number of threads per inch. "NF" stands for National Fine, a thread series specifying the thread form. "GH3" refers to the pitch diameter tolerance class, indicating the accuracy of the thread size. These taps are likely made in the USA, as suggested by the query. High-speed steel (HSS) is a common material for taps, offering durability and heat resistance. They are often used in machining and metalworking applications. The taps appear new and have a bright finish, which is typical for HSS tools. They're plug taps, meaning they have a full thread profile and are used for through holes or bottoming threads.