Tap & Clearance Drill Chart —
UNC, UNF, and Metric

UNC Tap and Clearance Drill Sizes

Unified National Coarse is the default thread series for general machined parts. Tap drill values are for cutting taps at approximately 75% thread.[1]

UNF Tap and Clearance Drill Sizes

Unified National Fine threads offer more engagement per length and finer adjustment. Common in aerospace hardware and thin sections. Clearance drills are the same as the equivalent UNC size.[1]

Metric Coarse Tap and Clearance Drill Sizes

Metric coarse tap drills follow the simple rule of nominal diameter minus pitch. Clearance values are the "normal" (medium) series per ISO 273.[2]

How to Use This Chart

Thread percentage. The tap drills above target roughly 75% of full thread height, the standard for cutting taps in common materials. Full 100% thread adds very little strength but multiplies tapping torque and tap breakage risk. In tough materials such as stainless steels, titanium, and nickel superalloys, shops often drop to 50 to 60% thread by drilling one size larger; the joint loses almost no strength and taps survive.[1]

Roll form taps. Form (roll) taps displace material instead of cutting it and need a larger hole than the chart values. A common approximation for 65% thread with a form tap is nominal diameter minus half the pitch. Check the tap manufacturer's recommendation before drilling.

Close fit vs free fit. Close fit suits dowel-adjacent hardware and parts that locate on their fasteners. Free fit is the default for general bolted assemblies and allows for position tolerance between mating parts. If holes on both parts are drilled free fit, standard fasteners assemble without fuss.

Thread depth. Threads deeper than about 2 to 3 diameters add cost without adding strength. See the thread guidance in our DFM Guide for CNC Milling for how depth callouts drive cycle time.