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What are counterbore and countersink? | PCB Knowledge

by: Jun 12,2023 1875 Views 2 Comments Posted in PCB Basic Information

Counterbore holes are cylindrical with flat bottoms, while countersink holes are conical recesses designed to accommodate a screw or bolt. Both types serve to insert screws or fasteners, yet they offer distinct characteristics and applications.

Figure 1: Countersink and Counterbore

Differences Between Counterbore and Countersink Holes


Counterbore holes are designed for screws or bolts with flat-bottomed heads that are larger than the screw’s body. This design entails creating a two-diameter hole with a larger diameter at the top to accommodate the head of the screw or bolt and a smaller diameter for the body of the screw or bolt.

On the other hand, countersink holes are suitable when the design requires a screw or bolt with a tapered head. These holes are drilled at a conical angle that matches the taper of the screw head, allowing the screw or bolt to sit flush with the surface of the PCB. When creating countersinks, a wide range of drill bits with different angles is available, commonly applied angles being 82 degrees and 90 degrees. It is always important to match the angle of the countersink hole with the tapered angle of the fastener being used.

Manufacturing Flexibility

Counterbore holes, due to their straightforward, vertical design, are typically simpler and easier to drill. However, this simplicity often corresponds to a lack of flexibility. Counterbore holes are tightly matched to the size and shape of specific screw heads, typically socket heads or hex head bolts. This may limit the options when using non-standard screws or customized mounting solutions in a PCB design. In contrast, countersink holes offer more adaptability due to their conical design, which can accommodate a broader range of screw sizes and types. This flexibility allows for various screw head sizes and shapes, providing more options for different applications.

Choosing Between Counterbore and Countersink Holes

When deciding whether to use counterbore or countersink holes, it's important to consider your design priorities. If saving space and maintaining flexibility is essential, countersink holes are usually the preferred option. By having the screws flush with the board, you can easily fit the PCB into space-constrained devices like watches or smartphones. Additionally, countersink holes provide a smooth surface design, which can be advantageous for aesthetic purposes or to prevent interference with other components.

On the other hand, if your primary concern is ensuring a secure and stable mounting of the board, even at the expense of space-saving or a sleek surface design, counterbore holes are the way to go. By using socket screws with counterbore holes, you can achieve a more robust and reliable connection, providing a stronger hold for the board.


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