Reference guide
UNC vs UNF Threads
How coarse and fine inch threads affect tap drill lookup and fastener selection.
UNC is coarse thread
UNC threads have fewer threads per inch. They are common for general fastening, rougher materials, and situations where assembly speed and tolerance for dirt or damage matter.
UNF is fine thread
UNF threads have more threads per inch. They often use a larger tap drill than the coarse version at the same nominal diameter because the thread depth is shallower.
The same diameter can need different drills
For example, 1/4-20 UNC commonly uses a #7 drill, while 1/4-28 UNF commonly uses a #3 drill. Always read the full callout, not just the nominal diameter.
Related references
Drill Size ChartFind fractional, number, letter, and metric drill sizes with decimal inch and millimeter equivalents.Tap Drill ChartLook up recommended tap drill sizes for UNC, UNF, and metric threads.Clearance Hole ChartCompare close-fit and free-fit clearance holes for common screws and bolts.Printable Drill Tap ChartPrint compact drill, tap, clearance, and pilot-hole sheets for shop use.