Modular Counterbore System

Counterbore systems (or counterbore drill bits) are used to make counterbore holes in almost any surface. Counterbore holes are perfect for creating space for heavy-duty screws and bolts.
Cromwell stocks a wide range of high-quality counterbore drill bits, from trusted brands used by professionals across the world.

What are counterbore systems?
Counterbore systems are used to make counterbore holes in almost any material. These holes are typically utilised to house a fastener within the workpiece, allowing them to be indented and sit flush with the surface.

Why a counterbore system?
Counterboring creates a perfect indentation within any material or workpiece. Unlike a countersink, a counterbore is a squarer shape, allowing for screw shoulders to fit comfortably. They are also deeper than countersinks, meaning there's room for bigger screws and washers.
A deeper bore allows for much stronger holding power than standard countersinks, and as such they are often favoured in heavy-duty applications.

When are counterbore systems used?
As counterbores are seen as the heavy-duty equivalent to countersinks, it's only natural that they are commonly used throughout heavy-duty industries. This includes:
• Automotive
• Aerospace
• Heavy machinery
• Construction

Types of counterbore system
When choosing a counterbore system, you'll notice a range of options to choose from alongside your standard counterbore systems. It's worth checking if any of the following are more suitable for your needs:
• Cap screw counterbore - Cap screw counterbores make room for the head of a standard head cap screw, hence the name 'cap screw'.
• Back counterbore - Back counterbores extend through the material you're cutting, providing a 'flipped' bore. This means the counterbored surface is on the reverse side of the chuck.
• Blade counterbore - Blade counterbores utilise blades on the side of the body to effectively cut materials.
• Aircraft counterbore - Aircraft counterbores are configured to cut the materials commonly used in the aerospace industry, such as aluminium and other non-ferrous metals.
If you're looking for the ideal counterbore system for your job but aren't sure about the best one for your needs, feel free to ask our experts for specialised advice.

Considerations when choosing a counterbore system
The most important consideration when picking a counterbore system is the material. Counterbores are available in a range of materials to suit various functions.
• HSS (High speed steel) is the most common material, due to its effectiveness across multiple common materials.
• Carbide counterbores are harder and more durable, however this comes at a price.
• Diamond tipped counterbores take this to the extreme, offering a very long working life and an extremely high cutting speed but at an even greater cost.
The trick is to find the ideal balance between tip hardiness and cost that makes sense for your usage.

Counterbore system jargon buster
Key ISO standards to look out for:
• ISO 4207:2016 - Specifies dimensions of counterbores, especially those with morse taper shanks and detachable pilots
• ISO 4206:2016 - Specifies dimensions of counterbores with parallel shanks
• ISO 9217:2002 - Specifies washer dimensions with counterbores for use in aerospace

What is counterbore spotface?
Counterboring and spotfacing differ slightly - unlike counterboring, spotfacing is always done at a right angle with the main axis of the hole.

What is the difference between countersink and a counterbore?
As previously mentioned, counterbores cut much deeper than countersinks, and cut a squarer, flat bottomed hole. Countersinks cut a cone-shaped hole that is not as deep.