UNF and UNF are symbols of Unified Screw Thread series. The Unified thread Series was agree on by the United States, Great Britain and Canada in 1949 to obtain interchangeability. Recently, modificatiosn have made to the original specifications for easy of use.
The unified Thread Series is classified into course threads, fine threads and extra fine threads much like Metric screw threads are.
- UNC: is the symbol for Unified Course pitch threads.
- UNF: is the symbol for the Unified fine pitch threads.
- UNEF: is the symbol for United extra fine pitch threads.
- UNS: is the symbol for Unified special threads.