Countersunk Screws

A countersunk screw, also known as a “flat-head screw,” sinks into a surface and rests flush in materials. Similar to other screws, a countersunk head screw has ridges that twist into a material to provide fastening power. Countersunk screws have a flat head instead of a rounded or semi-rounded one.

If you’re a contractor, you know that countersunk screws are valuable in woodworking applications to prevent splitting, cracking, gouging and other problem areas. Use a countersunk screw when you want to hide fixtures and maintain the integrity of the material.

Countersunk Screw Sizes

The sizes for a countersunk screw vary. The best way to determine size is to measure the threaded part of the screw with calipers. Based on that measurement, you can then select a slightly smaller drill bit to create a pilot hole.

Countersunk Screw Angles

The most common countersink angle for screws is 82 degrees based on the Unified Thread Standard. Countersinks, or tools with a cone-shaped end for modifying an existing pilot hole, are available with various angles to match a particular screw’s head angle.

How to Countersink Screws

A countersink drill lets you countersink screws with two different bit options. Fluted bits require two bits to make a pilot hole and a countersink hole. Combination bits can create both holes at once.

Fluted Bit

With a fluted bit, you use a regular drill bit to make a pilot hole and a second fluted bit to make a recessed area in the shape of a “V” for the screw. The steps involved are as follows:

1. Mark the hole position: Use a pencil and ruler to draw a small X. Consider using an awl or centerpunch to make a starting point for the drill bit.
2. Drill the pilot hole: Pick a drill bit based on the diameter of the screw.
3. Drill the countersink hole: Choose the bit based on the screw’s head size. Ensure that the hole is deep enough for the screw head to be flush.
4. Drive the screw: Use a screwdriver or drill to turn the screw into the hole.