Technical reference
A labeled reference for the dimensions and features used to describe taps — the length, angle, and cross-section terms you'll see on a spec sheet or print callout.
Complete tap terminology reference
What each labeled dimension and feature means.
The total length of the tap, from the tip of the point to the end of the shank.
The length of the unthreaded portion that's held by the tap wrench, holder, or machine spindle.
The length of the threaded, chip-cutting portion of the tap.
The length of the tapered lead-in at the tip, where the first few threads gradually cut to full depth.
The angle of that tapered lead-in. A shorter, steeper chamfer (like a bottoming tap) cuts closer to the bottom of a blind hole; a longer, shallower chamfer (like a taper tap) starts easier but needs more thread runout.
The centerline the tap rotates around — the reference line every diameter and angle is measured from.
The diameter of the shank, sized to match the tap holder or chuck.
The diameter at the very tip of the tap.
The perpendicularity of the shank and thread axis — how true the tap runs relative to its centerline.
The helix angle of the thread relative to the tap's axis, which affects chip flow and cutting action.
The center points used to hold and grind the tap true during manufacturing.
The usable threaded length available to engage the workpiece.
The width across the square drive at the end of the shank, used to key the tap into a wrench or holder.
How far the square drive extends along the shank.
The relief ground behind the cutting edge at the chamfer, which reduces friction and helps the tap cut rather than rub.
Tapping a tough hole? Browse tap lubricant and paste, or head back to the full terminology index for more terms.
Before you tap
Most tap failures start in the pilot hole and end with a seized flute. Get the hole right, then keep the tap cutting.