Counterbore vs. Spotface

What’s the Difference?

When machining holes for fasteners, you might hear about counterbores and spotfaces. They may look similar, but they serve different purposes. Let’s break it down!

What is a Counterbore?

A counterbore is a deeper, flat-bottomed hole that enlarges the opening of a smaller hole. Its job? To make space for the head of a screw or bolt so it can sit flush or below the surface. Think of it as creating a "seat" for your fastener to hide away neatly.

For example, if you’re assembling machinery and don’t want bolt heads sticking out, a counterbore is the perfect solution. It’s commonly used for socket cap screws in applications where precision and strength matter.

What is a Spotface?

A spotface, on the other hand, is like a shallow version of a counterbore. Its purpose is to create a flat, smooth surface around a hole so that fasteners or washers can sit evenly. This is especially helpful when working with uneven or rough surfaces, like cast parts.

Picture a bumpy surface where a bolt head can’t sit properly—spotfacing smooths out the area just enough to fix that problem.

How Are They Different?

Counterbore: Deeper, used to recess fasteners completely.

Spotface: Shallow, ensures fasteners sit evenly on rough surfaces.

If you want screws to be flush or hidden, go with a counterbore. If you just need a smooth area for the fastener to rest, choose a spotface.

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