How SDS Drill Bits Work: Shank, Flutes and Carbide Head Explained

SDS drill bits are the standard consumable for rotary hammers on US job sites. For distributors, private-label brands and contractors buying in volume, understanding how each part of the bit works makes it easier to write a clear specification and compare quotes on equal terms.

The SDS shank: why the bit slides

An SDS shank has open grooves that the hammer’s chuck locks into and closed grooves that hold the bit in place. The bit can slide back and forth a short distance in the chuck. That movement is the point: the hammer’s piston strikes the end of the shank, and the impact travels straight down the bit to the tip instead of being absorbed by a tightened chuck.

• SDS-Plus: 10 mm shank, used on light and medium rotary hammers for anchor holes and holes up to about 1 in (26 mm).
• SDS-Max: 18 mm shank, used on heavier hammers for large anchors, through-holes and long reaches.

Shank dimensions and groove geometry need to be held tightly. A shank that is out of tolerance wears the chuck, wastes impact energy and produces customer complaints that are hard to trace back to the bit.

The body and flutes: moving dust out

The body is usually a heat-treated alloy steel such as 40Cr. It has to be hard enough to resist bending and fatigue under constant hammering, but not so brittle that it snaps. On our standard builds the body is heat-treated to about 48–53 HRC.

The flutes carry dust out of the hole. Two-flute designs are simple and economical; four-flute (S4-style) designs move dust faster and keep the head cooler, which matters for deep holes and high-volume drilling. Flute shape, pitch and depth are all specification points you can set on a made-to-print order.

The carbide head: where the cutting happens

The tip is tungsten carbide brazed or welded into the steel body. Common grades such as YG8C (tungsten carbide with about 8% cobalt) balance wear resistance with toughness. Head geometry affects performance:

• 2-cutter (single plate): fast in brick and block, economical for general anchoring.
• 4-cutter (cross or X head): rounder holes, less jamming when the bit meets rebar, longer life in reinforced concrete.
• Centering point: helps the bit start accurately without walking on hard surfaces.

Braze quality is one of the biggest causes of field failure. On made-to-print orders we agree braze inspection and tip-retention checks as part of the sample approval.

Diameter tolerance and anchor fit

For anchoring, the tip diameter decides whether a wedge anchor or concrete screw holds to its rated load. US buyers often reference ANSI B212.15 tolerances for carbide-tipped masonry drills. If your customers install anchors, include the tip tolerance on your drawing and ask for measurement data with the sample.

What to include in your specification

• Shank type (SDS-Plus or SDS-Max) and diameter and length range, in inch, metric or both
• Head type (2-cutter or 4-cutter) and carbide grade
• Body steel and hardness range
• Flute design
• Tip tolerance standard
• Marking, coating, packaging and barcode labeling
• Annual volume and target delivery terms

What does SDS stand for?

SDS comes from the German Steck – Dreh – Sitz (“insert – twist – fit”), the bit-holding system developed by Bosch. In English it is often expanded as “Slotted Drive System” or “Special Direct System”. In practice it means a bit with grooves in the shank that clicks into a rotary hammer’s chuck without tightening and slides back and forth so the hammer’s impact reaches the tip.

SDS drill vs hammer drill: what is the difference?

A hammer drill uses a standard keyed or keyless chuck that grips a round or hex shank, and creates impact with two ridged discs (a clutch mechanism). It suits small holes in brick and block. An SDS rotary hammer uses an electro-pneumatic piston and an SDS chuck, which delivers much more impact energy per blow. It drills concrete faster and with less effort, and can also chisel. SDS bits only fit SDS hammers; straight-shank masonry bits fit hammer drills.

	Hammer drill	SDS rotary hammer
Bit shank	Round or hex, tightened in chuck	SDS-Plus (10 mm) or SDS-Max (18 mm), click-in
Impact mechanism	Clutch discs	Electro-pneumatic piston
Best for	Small holes in brick, block, light concrete	Concrete, reinforced concrete, anchors, through-holes
Chiseling	No	Yes (with SDS chisels)