Hammer Drill Bits Explained

Hammer drill bits are designed to withstand the intense pressure and pounding action of hammer drills. Most have carbide tips on hardened steel bodies, built for durability and strength.

Which bit you choose affects how fast you drill, how long the bit lasts, and, for relative humidity testing, whether the hole fits the sensor. Two kinds of tools drill concrete with a hammering action: hammer drills and rotary hammers. Rotary hammers hit harder and are the usual choice for drilling concrete. Demolition hammers and chipping hammers only pound and are used for breaking concrete, not drilling it.

In this article we’ll cover what a hammer drill bit is, the types available, the anatomy of a bit, and what makes a good RH test hole.

• What Is a Hammer Drill Bit?
• What Type of Drill Bits Are Used With a Hammer Drill?
• Are All Hammer Drill Bits Created Equal?
• The Anatomy of a Hammer Drill Bit
• Drill Bit and Its Role in the Hole
• Ensuring the Best RH Test Hole
• FAQs

What Is a Hammer Drill Bit?

Hammer drills are designed to drill quickly through brittle materials like concrete by combining the rotation of the drill bit with a hammer action that drives the bit in and out along its axis.

They work with a couple of different mechanism designs, but ultimately the drill is only as effective as its bit. With that dual action in a tough material like concrete, the drill bit itself has to withstand a lot of force.

What Type of Drill Bits Are Used With a Hammer Drill?

The kind of bit you’ll need largely depends on the material you’re working with. Here’s a rundown of bits commonly used with hammer drills:

Masonry Bits

These are the go-to bits for hammer drills. Their carbide tips break up hard materials like concrete, brick, and stone.

SDS Bits

SDS bits (SDS-plus and SDS-max) are masonry bits with a slotted shank designed specifically for rotary hammers. The shank locks into the drill securely while still letting the bit slide back and forth with the hammering action.

Spade Bits

Spade bits are for drilling larger holes in wood, not masonry. If you use one in a hammer drill, switch the hammer function off and use rotation only.

Equipping your hammer drill with the appropriate bit is crucial for good drilling performance, for the life of your tool, and for the success of your project.

Are All Hammer Drill Bits Created Equal?

In basic anatomy, maybe.

However, on the job site, several small factors can add up to a better experience when drilling concrete. Different materials have been developed to provide both hardness and strength to improve the drill bit’s performance, and the type or make of drill you are using will steer your bit choice as well.

So let’s look at the basic anatomy of a hammer drill bit and what is necessary for complete and accurate relative humidity (RH) concrete testing.

The Anatomy of a Hammer Drill Bit

The Shank

The shank is the portion of the drill bit that fits into the hammer drill and holds it securely as the drill provides both rotation and impact during operation. For most rotary hammer drills, a smooth shank is insufficient because the drill bit can slip during operation and come loose from the drill itself.

Common shank designs for rotary hammer drills include SDS-plus, SDS-max, and spline shanks that lock into the chuck so that the action of the hammer drill will not dislodge the drill bit.

The Land

The land is the raised portion of the spiral on the drill bit. The land holds the cutting edges of the bit on its outside diameter.

The Flute

The flute on a drill bit is the “trough” that runs alongside the land. Its purpose is to carry dust out of the hole as it is being drilled to prevent jamming.

The Head

The head is the lead end of the drill bit that holds the carbide tip and does the work of breaking up the concrete. Depending on the tip design, it has either two or four cutting edges.

The Tip

For concrete drill bits (and others), carbide is brazed to the drill bit head to harden and strengthen it for breaking up the concrete. Excessive heat in the hole can weaken the braze that holds the carbide in place or crack the carbide, dulling the bit and reducing its ability to break the concrete.

Drill Bit and Its Role in the Hole

Regardless of the hammer drill bit’s precise composition, the basic elements are the same, and for concrete moisture testing its job is the same: to drill a precise test hole in a concrete slab that will hold the RH sensor for accurate RH, or in situ, testing of the slab’s moisture conditions.

The depth and the width of that hole play a role in providing accurate RH data to building inspectors, flooring installers, and the other professionals responsible for a lasting, serviceable concrete slab.

Ensuring the Best RH Test Hole

A rotary hammer drill bit is a key part of preparing a concrete slab for RH testing, and because a precise test hole will help ensure the best fit for the RH sensor, technique matters too.

Test Hole Depth

ASTM F2170 says the sensor location (and, therefore, test hole depth) must be at 40% of the slab depth when the slab is drying from one side and 20% when it is drying from two sides.

We recommend marking that depth on the drill bit with a tape “flag” that lets the drill operator see when they have reached the right depth. Holding the hammer drill straight up and down keeps the hole straight and gets the best performance from the drill and bit.

Test Hole Width

RH test system manufacturers supply precise specifications for their test hole widths as well. For example, Rapid RH^® Smart Sensors go in a hole drilled with a ¾” masonry bit, and a 4-fluted, carbide-tipped bit that falls within the ANSI B212.15 specification for a ¾” masonry bit works well.

That range is from 0.775” to 0.787”. If your drill bit is at the lower end of this specification, the sensor might be a tight fit that is difficult to install correctly.

Experience suggests that bits with four cutting edges produce a rounder hole, making it easier to seat the RH sensor. Wagner sells an SDS-plus masonry bit (the Hilti TE-CX) for Rapid RH test holes and also recommends the Hilti TE-CD hollow drill bit, which vacuums dust out as it drills so the hole is clean when you’re done.

Of course, the other reason for a tight fit could be that your drill bit has worn down with use and lost some of its diameter. Check the bit’s diameter periodically, especially after it has drilled many holes.

A worn drill bit also increases the risk of the bit jamming in the hole because it can no longer clear the dust efficiently. Before each job, visually examine the drill bit’s head and flutes to make sure they were not damaged on a previous job.

RH testing provides accurate, ASTM F2170-compliant concrete moisture measurement, and the hammer drill bit is a vital component of the process.

Hammer drill bits are essential tools for drilling through rigid materials like concrete. Their durable construction and specialized design allow them to withstand the intense pressure and pounding action of hammer drills.

You can ensure efficient and effective drilling for your construction or DIY projects by choosing the right bit and properly maintaining it.

And when it is time to drill your test holes, start with the right bit.

Shop Masonry Drill Bit

Shop Rapid RH

FAQs

How Do I Know Which Bits Fit My Hammer Drill?

Check the shank type first. Rotary hammers take bits with a specific shank system, and the drill’s specifications will list which one it accepts.

The most common are SDS-plus, which has a 10 mm shank and is used on lighter rotary hammers, and SDS-max, which has an 18 mm shank and is used on larger, heavier rotary hammers. Some older or heavy-duty drills use spline shanks. If you’re not sure which shank a bit has, compare it to the drill manufacturer’s specifications or measure the shank diameter with a caliper.

Last updated on October 7th, 2026