The Unified Coarse thread series (UNC/UNRC) is used for the bulk production of screws, bolts and nuts. It is commonly used in relative low strength materials such as cast iron, aluminum, magnesium, brass, bronze and plastic, because the coarse threads provide more resistance to internal thread stripping than the fine or extra fine series. The fine thread series (UNF/UNRF), is commonly used for bolts and nuts in high strength applications. Fine series threads allow for finer adjustment in cases such as slotted nut and cotter pin assembly.
The extra-fine series (UNEF/UNREF) is used particularly for equipment and threaded parts which require fine adjustments, such as bearing retaining nuts, adjusting screws, etc. and for thin wall tubing and thin nuts.
