What is the different of unf thread and unc thread? 1. UNF, UNC; is the identification of inch uniform thread 2. UNF is the abbreviation of "du" for the English Unified National Fine, which is the series of zhi unified spiral dao pattern fine teeth. UNC is the abbreviation of Unified National Coarse in English, which is a series of unified thread coarse teeth. 3. Coarse teeth seem to have large teeth, with fewer teeth per unit length, and fine teeth, with smaller teeth, and more teeth per unit length.