When it comes to machining, countersink and counterbore holes are two essential types that serve distinct purposes. While their shapes may be the most noticeable difference, there are other key aspects worth exploring. Let’s dive deeper into these hole types, their uses, and how they compare.

What is a Countersink Hole?

Countersink holes, indicated by the symbol “⌵,” are cylindrical holes designed to accommodate the angle of a screw, allowing it to sit flush with the surface. Commonly found in woodworking and soft materials, these holes can have various angles, typically ranging from 60° to 120°, with 90° being the most common.
The cone-shaped design of a countersink hole features a widest part known as the "Major Hole Diameter," specifically tailored for the insertion of screws or bolts. The angle of the hole plays a crucial role; a deeper sink enhances the fastener's grip, making joints stronger while minimizing the risk of stripping the material.
Countersinks can be created using a drill and a Phillips-head bit, or with specialized tools. They are particularly advantageous for sheet metal applications, where counterbores may be too costly.

What is a Counterbore Hole?

Counterbore holes, represented by the symbol “⌴,” also take a cylindrical form but are designed to widen a hole’s opening and create a flat bottom. This design allows fasteners, particularly socket-head screws, to sit flush or even below the material's surface. The walls of counterbore holes are straight and maintain a 90° angle from the surface.
Creating a counterbore hole involves drilling a smaller pilot hole first, followed by enlarging it with a counterbore cutter, which is a type of end mill. If made large enough for a washer, counterbore holes can significantly improve holding power. .

Countersink vs. Counterbore Holes

The primary differences between countersink and counterbore holes lie in their depth and shape. Counterbore holes tend to be shallower and have straight sides, offering more holding strength for several reasons: the force from the socket cap screw head is aligned with the axis, and the load is distributed over a broader surface area. In contrast, countersink holes feature tapered sides, leading to uneven force distribution.
Countersinks are ideal for wood and metal screws, while counterbores are typically used for larger fasteners like lag bolts. The choice between the two often depends on the size of the pilot hole; countersinks usually require smaller pilots, making them more suitable for lightweight applications, while counterbores are preferred for heavy-duty tasks in construction, machinery, and automotive contexts.

Key Specifications

When considering these holes, it’s essential to understand their dimensions. Sizes are typically defined by diameter (width of the hole), depth (distance from the material surface to the top of the pilot hole), and the angle of the countersink. Counterbore sizes generally range from 3/16” to 1”, while countersinks range from 1/16” to ½”. Always consult a standard size chart to ensure accuracy.
Other Types of Machining Holes Countersink and counterbore holes are just a couple of the many types available in machining. Here are a few others to consider:


• Blind Hole: A type of counterbore that doesn’t go all the way through the workpiece.

• Simple Hole: Passes completely through a material and is used for fastening parts together.

• Counterdrill Hole: Contains a countersink that is recessed below the surface.

• Tapped Hole: Created through tapping to cut threads into the hole’s walls, useful as an alternative to nuts and bolts.

• Spotface: A shallow counterbore with a smooth finish.

Versatile Size Range

Samtec Taps are available in a wide range of sizes, from M2 to M36. This versatility means that they can meet all your threading needs, whether you are working on small, delicate components or larger, more robust parts. The comprehensive size range makes Samtec Taps a one-stop solution for all tapping and threading applications in precision engineering.

Premium and High-Performance Tapping and Thread Cutting & Forming Taps

Optimal for Blind Hole Applications

Blind hole applications are particularly challenging due to the difficulty of removing chips and ensuring a clean, precise thread. Samtec Taps are designed to excel in these scenarios. Their advanced design helps eliminate chip clogging, keeping operations smooth and efficient. This makes them an ideal choice for precision engineering tasks that require tapping into blind holes.

How SAMTEC Can Help

At SAMTEC, we provide comprehensive machining solutions, including drilling, grooving, threading, and more. Our offerings include a variety of tools, such as Manual and Machine countersinks, deburring systems, and specialized cutting tools, designed to meet all your machining needs.
Whether you’re looking solution for countersink and counterbore holes or need a free, no-obligation quote, contact a SAMTEC representative today. Let us help you with your next machining project!