Tap and drill chart

A threaded fastener is a type of mechanical fastener that features helical grooves (threads) on its exterior, such as a bolt or screw, or its interior, such as a nut. These threads engage with corresponding threads on a mating component or in a tapped hole, creating a clamping force that securely joins two or more parts.

These fasteners typically adhere to standardized thread systems, most commonly the Unified Thread Standard or the ISO Metric Thread System.

Tap and die sets use cutting tools, taps for internal threads in holes and dies for external threads on cylindrical stock, to remove material and create the helical profile. Taps come in taper, plug and bottoming styles, which differ in how many threads at the tip are chamfered away and therefore how close to the bottom of a blind hole each one can cut.

Rolling processes form threads by plastically deforming the material instead, which often results in stronger threads with a smoother surface finish. Nothing is cut away, so there are no chips to clear, and the grain of the stock follows the thread form rather than being severed by it.

Every number in the tables below is one of these diameters. The tap drill leaves the female minor diameter behind; the clearance drill has to clear the male major diameter.

Major and minor are the easy two to picture, out at the crests and down in the roots. Pitch diameter sits between them, and because it is where the flanks bear on each other, it is the one that decides whether a fit comes out loose, snug or tight.