Sets for American inch threads
Eight compositions of hand taps and dies in DIN design from HSS-G, for internal and external threads. UNC from 1/4 to 1.1/2 inch, UNF from 1/4 to 1 inch, plus a combined set with both series from 1/4 to 3/4 inch.
UNC or UNF?
UNC is the coarse thread and plays the role of the metric coarse thread: the standard choice for commercial screws and nuts. UNF is the fine thread with the same profile but a smaller pitch. It holds better against vibration and allows finer adjustment, but tolerates less dirt in the thread. Both have a flank angle of 60°, like the metric ISO thread.
The designation
In 1/4-20 UNC, 1/4 is the outside diameter in inches and 20 the number of threads on one inch. The pitch in millimetres is 25.4 divided by the thread count, here 1.27 mm. Diameters below 1/4 inch carry numbers instead of fractions.
Which set to take?
For most work the range 1/4 to 1/2 inch is enough. Anyone working on American machines or vehicles soon reaches 3/4 inch and beyond. When both series occur, the combined UNC/UNF set from 1/4 to 3/4 inch saves the second case.
Do not confuse with Whitworth. BSW and BSF have a flank angle of 55° and rounded crests. On some sizes the thread count matches UNC, yet they are still not interchangeable. For British threads there are separate sets under assortments.
Single tools in UNC and UNF are under hand taps and round dies.
