Drill Nomenclature: The Complete Parts Reference

Walk into any machine shop and ask someone to name every part of a twist drill. Most can name five or six. There are closer to twenty distinct features on a standard twist drill, and each one serves a specific purpose. Knowing the names is useful for communication — but understanding what each feature does is what lets you diagnose problems, specify geometry correctly, and have productive conversations with resharpening vendors.

The Shank

The shank is the end of the drill that mounts in the toolholder. Straight shanks are cylindrical and held in a chuck or collet. Taper shanks (Morse taper) self-lock in the spindle via the taper angle and are used for larger drills that require more driving torque than a straight-shank chuck can reliably transmit.

The shank diameter on some drills is slightly smaller than the body diameter — this is intentional on reduced-shank (or reduced-neck) drills that allow large-diameter drills to mount in smaller chucks. Always verify you are holding the shank, not the body, in your toolholder.

The Body

The body is the main cutting section of the drill, from the beginning of the flutes to the tip. It contains most of the geometry that determines cutting performance.

Flutes are the helical grooves running along the body. They serve two purposes: they form the cutting edges at the tip, and they are the pathway through which chips travel from the cutting zone to the outside of the hole. Flute geometry — helix angle, width, depth — determines how efficiently chips clear.

The helix angle is the angle of the flutes relative to the drill axis. Standard helix is approximately 29-30°. High helix (40°+) moves chips faster and is better for soft, gummy materials like aluminum. Low helix (15-20°) provides more rigidity and is better for hard, brittle materials like cast iron and brass.

Lands are the narrow raised surfaces between the flutes. The land follows the helix of the flute. The outer surface of the land is the margin — the narrow cylindrical band that contacts the hole wall as the drill advances. The margin provides guidance and burnishing of the hole wall surface.

Behind the margin, the land is relieved (reduced in diameter) to reduce friction between the drill body and hole wall. This relief is called the body clearance. Without body clearance, the entire land surface would rub against the hole wall, generating heat and requiring enormous torque.

The web is the solid central core of the drill connecting the two flutes. Web thickness increases from tip to shank for rigidity. A thicker web is stronger but creates a wider chisel edge requiring more thrust force to penetrate. Web thinning reduces chisel edge width by grinding additional relief behind the point.

The Point

The point is the tip geometry that actually initiates cutting. It contains several distinct features.

The cutting lips (also called the cutting edges or lips) are the two main cutting edges formed by the intersection of the flute face and the point relief surface. The cutting lips remove the bulk of the material.

The chisel edge is the short straight edge connecting the two cutting lips across the web at the very tip. As discussed in our geometry article, the chisel edge scrapes rather than cuts and accounts for a disproportionate share of required thrust force.

The point angle is the included angle between the two cutting lips. Standard is 118°; harder materials typically use 135°.

The lip relief angle (clearance angle) is the angle of the surface immediately behind each cutting lip, providing clearance so only the edge contacts the work.

The face is the flute surface that contacts the chip during cutting. Chip curl and chip flow are influenced by face geometry.

Sizing and Classification

The overall length is the total drill length from tip to shank end. The flute length is the length of the cutting portion. Jobber length drills are the standard proportion — a ratio of flute length to diameter that balances rigidity against reach. Screw machine length (stub) drills are shorter for rigidity. Long series (taper length, extra-long) drills sacrifice rigidity for reach.

Understanding all these features together lets you read a drill like a diagnostic report. Chipped lips suggest incorrect lip relief or hard material contact. Worn margins indicate a hole that is too tight or inadequate coolant. Heavy wear behind the lips without lip damage suggests proper cutting with the chisel edge as the failure point — a web thinning problem. Every wear pattern tells a story about the process.