Cutting diameter tolerances: 1/32" through 31/64": +. 0002", - Cutting diameter tolerances:  1/32" through  31/64": +.0002", -.0000";  1/2" through  19/32": +.0003", -.0000";  5/8" through 1 1/2": +.0005", -.0001".

Fastener dimensions The head style and type. The length required specified in inches, fractions of inches or millimeters. The diameter - when measuring in inches for diameters less than 1/4" there is a gauge number, above that specify the diameter in fractions of an inch. For metric the diameter is specified in millimeters. The thread pitch - distance between threads or threads per inch. UNC, UNF and Metric define standard values. The material - brass, stainless steel, nylon etc.

http://www.americanfastener.com/technical/thread_terminology.asp

http://www.machinist.org/harvard_cotreau/mshop6.html