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Straight Shank vs Reduced Shank vs Morse Taper Drill Bits

Every HSS twist drill has a cutting end and a holding end. The holding end — the shank — determines how the drill connects to the machine, how torque is transmitted, and ultimately what diameter range the drill can cover. In industrial metalworking, two shank systems dominate: the straight (cylindrical) shank and the taper (Morse Taper) shank. Choosing the wrong one does not just mean poor performance — it means the drill physically will not fit your machine.

This guide provides a complete technical comparison for procurement engineers, workshop managers, and distributors who need to stock the right drills for their customers’ machines.

Two Shank Systems for Two Worlds of Drilling
The straight shank and taper shank are not competing designs — they are complementary systems engineered for different machine types, diameter ranges, and production environments.

Straight shank drills (DIN 338, DIN 340, DIN 1897) are held by a 3-jaw chuck or collet. The chuck jaws clamp around the cylindrical shank with radial pressure. This system is universal: any straight shank drill fits any 3-jaw chuck within its capacity range (typically 1–13 mm or 1–16 mm). Straight shank drills are the standard for hand drills, drill presses, and CNC machining centers.

Taper shank drills (DIN 345, DIN 1870) use a Morse Taper (MT) — a precision-ground conical shank that is pressed into a matching taper bore in the machine spindle. There is no chuck. The drill is held by friction between the two tapered surfaces, with a tang at the end that engages a slot for ejection. Taper shank drills are the standard for radial arm drills, lathes, milling machine spindles, and heavy-duty drill presses.

The choice between them is almost always dictated by the machine you have, not personal preference. A radial drill press with an MT4 spindle cannot accept a straight shank drill without an adapter (which degrades performance). Conversely, a CNC machining center with ER collet holders has no use for a taper shank.

Structural Differences: How Each Shank Works

Straight Shank — Chuck Grip
A straight shank drill has a perfectly cylindrical shank ground to h8 tolerance (for fully ground drills) or h10 tolerance (for rolled drills). The shank diameter equals the drill diameter for sizes up to 13 mm. Above 13 mm, the shank is often reduced to 13 mm (called a reduced shank or blacksmith drill) to fit standard chucks.

The 3-jaw chuck applies radial clamping force from three equidistant jaws. Torque is transmitted entirely through friction between the jaws and the shank surface. This means:

If the chuck is worn or not tightened sufficiently, the drill can spin inside the chuck (slipping), scarring the shank and ruining the hole.
The maximum torque the system can handle is limited by the clamping force of the chuck, not the shank itself.
Runout (eccentricity) depends on the quality of the chuck — a precision keyless chuck can achieve 0.02 mm TIR, while a cheap chuck may allow 0.1 mm or more.
For CNC applications, straight shank drills are held in ER collets, Weldon holders, or hydraulic chucks rather than 3-jaw chucks, providing far better grip and precision.

Taper Shank — Friction Taper Self-Locking

A taper shank drill has a conical shank ground to a precise Morse Taper profile (approximately 1.5 degrees included angle, varying slightly by MT number). When the taper is pushed into the matching bore of the machine spindle, the large surface area of the taper creates a friction lock that resists both rotation and pullout.

Key features of the taper shank system:

Self-locking: The slight taper angle (roughly 5/8″ per foot for most MT sizes) means the drill wedges tighter as axial force increases. The harder you push, the stronger the grip.
Tang: A flat tab at the end of the taper engages a cross-slot in the spindle bore. The tang prevents rotation only as a safety backup — the primary torque transmission is through the taper friction. The tang also provides a surface for the drift key to eject the drill.
No chuck needed: The taper-to-bore connection is the entire holding mechanism. This eliminates the chuck as a source of runout and removes the maximum diameter limitation of the chuck.
Rigidity: Because the drill shank is in direct contact with the machine spindle bore along its entire taper length, the system is inherently more rigid than a 3-jaw chuck, especially for large diameters.

Where Reduced Shank Fits

A reduced shank drill sits between the two main systems. The cutting diameter is larger than the shank, so a 16 mm, 20 mm, or sometimes 25 mm drill can still fit a 13 mm or 16 mm chuck. That is convenient for maintenance teams and small workshops, but it does not create the same rigidity or torque capacity as a Morse taper.

Buyer situation Reduced shank decision Risk to check
Occasional larger hole on a 13 mm chuck drill press Can be practical for low-volume work Chuck slipping and operator wobble
Repeated 18-25 mm holes in steel plate Move to Morse taper if the machine allows Torque demand can exceed chuck grip
Retail or maintenance assortment Useful as a limited convenience SKU Do not present it as heavy industrial tooling
Production drilling Prefer straight shank in proper holders or DIN 345 taper shank Runout and inconsistent hole quality
For distributors, reduced shank is best treated as a convenience bridge, not a replacement for taper shank drills. It belongs in maintenance and jobsite assortments, while DIN 345 Morse taper remains the better option for stable, repeated large-diameter drilling.

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