This part of BS 1580 specifies limits of sizes, and tolerances, for
single-start, clearance-fit unified screw threads, in inch units, with
nominal diameters in and above, having the ISO basic profile as
specified in BS ISO 68-2:1998.
The part of BS 1580 specifies the following unified thread series as
follows:
a) standard variable pitch series:
• a coarse thread series (UNC) from 1/4 in to 4 in nominal
diameter;
• a fine thread series (UNF) from 1/4 in to 3/2 in nominal diameter;
• an extra fine thread series (UNEF) from 1/4 in to 27/16 in nominal
diameter;
b) standard constant pitch series:
• a 4-threads per inch series (4 UN) from 21/8 in to 6 in nominal
diameter;
• a 6-threads per inch series (6 UN) from 23/16 in to 6 in nominal
diameter;
• an 8-threads per inch series (8 UN) from 17/16 in to 6 in nominal
diameter;
• a 12-threads per inch series (12 UN) from 5/8 in to 6 in nominal
diameter;
• a 16-threads per inch series (16 UN) from 7/16 in to 6 in nominal
diameter;
• a 20-threads per inch series (20 UN) from 5/16 in to 3 in nominal
diameter;
• a 28-threads per inch series (28 UN) from 5/16 in to 3/2 in
nominal diameter;
• a 32-threads per inch series (32 UN) from 7/16 in to 1 in nominal
diameter;
c) a special thread series (UNS) with diameter/pitch combinations
other than those specified for the standard series.