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  • Writer's pictureNaoki Shibata

What is "Counterboring / Countersinking" ?

Updated: Jun 1, 2022

Counterboring (also called Countersinking) is a necessary process to prevent bolts and screws from loosening, improve aesthetics, and prevent injuries. The counterboring completely hides the screw head and prevents the screw from coming loose if it hits or gets caught on something.

By machining the bolt heads to fit inside the seat surface, the finish is flat when viewed from the side.

The main bolt for which a counterbore is used is the "hexagon socket bolt. These bolts have a hexagonal hole in the center of the head and are tightened with a hexagonal wrench.

Most hexagon socket head bolts have long heads, which, without a counterbore, protrude considerably from the seating surface. This can cause injury or make it easier for the bolt head to catch and loosen the screw.

Therefore, it is common to make a counterbore when using hexagon socket head bolts.

We, E&H Precision Asia's Largest CNC Machining Metal Lathe Turned Parts Manufacturer in Japan, Thailand, India is able to process Counterboring for any metals like steel, stainless steel, brass, copper, aluminum.

Please feel free to Contact Us for free quotes, or take a look at Our Factory Virtually , or Subscribe Monthly Newsletter which includes the Industry Reports and Technical Trends.


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