What Is a Countersink Drill Bit?

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It won’t take you long to discover a need for countersinking a screw in one of your DIY projects. By countersinking, you are able to achieve several objectives. It hides the fastener while preventing tear-out, along with eliminating deburring hazards.

What is a Countersink Drill Bit?

A countersink drill bit is a specialty accessory for drills, used to make a cone-shaped depression in wood. Countersink drill bits are used when the top of the fastener should sit flush with the surface of the material.

Countersink drill bits are often used to prepare pilot holes in hardwood. They can also be used with metal and plastic.

An image of what a countersink drill bit looks like

Types of Countersink Bits

There are two main types of countersink bits: combination and one-piece. One-piece countersink drill bits can be further differentiated into fluted and cross-hole styles.

Combination

Combination countersink bits usually have two ends. One side is used to drill the pilot hole and form the countersink. The other side is used to drive the fastener into the wood. Combination countersink bits are great for ensuring that your pilot hole is the appropriate size for your screw.

One-Piece

One-piece countersink bits, as the name suggests, consist of a single piece. You will need to drill the pilot hole first, then switch bits to create a countersink.

Fluted or Cross-hole

Grooves or tunnels in the body of the bit allow wood chips to escape during use. When these groves are on the outside of the bit, they are known as flutes. Cross-hole countersink bits eject debris through an angled tunnel bored through the middle of the bit.

Countersink Drill Bit Tools

Multiple tools can be fitted with a countersink drill bit. They include power screwdrivers, handheld drills, and drill presses.

Power Screwdriver

A power screwdriver can be used to countersink fasteners, provided an appropriate drill bit is used. The countersink drill bits that are compatible with power screwdrivers have a hexagonal shaft.

Handheld Drill

Handheld drills are the tool used most often to make a countersunk pilot hole. A handheld drill with a universal three-jawed chuck is compatible with cylindrical shank countersink drill bits.

Drill Press

With an appropriate bit installed, a good drill press can also be used to form countersinks in the surface of materials such as wood, plastic, or even metal.

A man using countersink drill bit

Countersink vs Counterbore? 

Both a countersink and a counterbore are receptacles for fasteners that allow the head of the fastener to disappear into the material, or sit flush with its top surface. 

In a countersink, the top portion of the hole is the widest point. The walls of the hole taper down to the approximate size of the fastener, forming a cone or funnel shape. Countersinks are generally used to conceal screws and bolts.

The topmost portion of a counterbore is also the widest point, but the walls do not taper. The resulting flat-bottomed hole can conceal washers and nuts.

Can You Countersink With a Regular Drill Bit? 

If you are drilling into a softwood, it’s possible to sink the head of your screw below the wood’s surface using a regular drill bit. However, splintering and tear out around the screwhead is difficult to avoid. If you want a smooth, attractive surface after joining two pieces of wood, you should use a properly shaped countersink drill bit.

If you are drilling into hardwood, a regular drill bit will usually not be able to force the head of a screw below the surface of the wood. Choose a countersink bit instead to drill a pilot hole with a smooth depression that can accept a screw without spitting up splinters.

When to Use a Countersink Drill Bit 

There are several scenarios where it makes sense to use a countersink drill bit, such as when you want to hide fasteners, prevent tear-out, eliminate safety hazards, or deburr material. 

Hide Fasteners

By drilling a countersink that is slightly deeper than the head of the fastener, you create the possibility to hide the fastener entirely. Wood plugs, wood filler, or even spackle can be used to fill in the hole, covering the fastener head and giving the appearance of smooth, undisturbed wood. 

Prevent Tear-Out

The threaded body of a screw cuts through wood as it is propelled forward. The head of the fasteners is unthreaded. Instead of cutting the wood, it tends to grab and pull wood fibers, creating a mess known as tear-out. 

Tear-out is especially common when inserting fasteners into hardwood. For best results, the countersunk pilot hole should be the same size as the tip of the screw or fastener you will be inserting.

Eliminate Hazards

On a smooth surface, a protruding screw or other fastener poses usability issues. On a floor, they are a stumbling hazard. Screwheads that stick out can snag fabric or scratch hands. Countersinking your fasteners will remove these dangers. 

An image of what a countersink drill bit looks like

Deburr Material

Drilling a hole through metal or plastic can create burrs. A burr can be defined as an unwanted protrusion of material, created through machining. 

A countersink drill bit can be used to deburr the sides of the hole by removing the burred portion. 

Learn more in my guides on drill bit sizes:

How to Choose and Use Drill Bits | Ask This Old House

Conclusion

Countersink drill bits are used to make countersinks in wood. A countersink is a conical depression used to hide the head of your screw. Countersink bits are most often used to prepare pilot holes in wood, but can also be used to deburr holes in metal or plastic.

Ellenkate grew up on job sites run by her family’s construction company. She earned her theater degree from The Hartt School, a prestigious performing arts conservatory in Connecticut. Her design and DIY work from her Chicago loft was featured in the Chicago Reader and on Apartment Therapy.