This part of BS 1580 specifies limits of sizes, and tolerances, for
single-start, clearance-fit unified screw threads, in inch units with
diameters 1/4 below in.
This part of BS 1580 specifies unified screw threads from
Number 0 (0.060 in diameter) to Number 12 (0.216 in diameter),
known as the “numbered sizes” in the following standard series:
• a coarse thread (UNC) series;
• a fine thread (UNF) series;
• for Number 12 threads, an extra fine (UNEF) 32 threads per inch
diameter/pitch combination.
NOTE Unified screw threads below 1/4 in diameter for attachment
purposes and for general use in the aircraft industry are specified in
Annex A.