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What is a square file?

What is a square file?

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Image of a narrow slot in a piece of metal that could easily be deburred with a square file Square files are machinist’s files that can be used in slots and key ways.
Image of a DIYer using a square file to rapidly remove material from the inside of a circular hole They are also used for roughing (removing material quickly) when turning round drill holes into square slots.

For a step by step guide, see: How to square a round hole with files

What are the characteristics of a square file?

Diagram of a square cross section

Cross section

As the name suggests, square files have a square cross section.

Image of a square groove that has been cut by a square file This means that they can be used to file square or rectangular notches in a workpiece.
Image of a right angled notch that has been cut by a square file They can also be used to create right-angled notches by turning the file to cut with its corner (edge).
Image showing the outline and cut of a square file


They taper in both width and thickness.

Image of a wooden hard drive case with a hole in the front that has been enlarged to the correct dimensions by use of a square file This enables them to be used to enlarge square holes.
A double cut file, which has grooves cut in two directions


They are double cut on all four faces, allowing them to remove material with multiple faces with equal speed.

An indication of the range of lengths in which square files are usually available


Square files are usually available in lengths from 100mm (4 inches) to 350mm (14 inches).

American and Swiss flags, illustrating that this type of file is made in either American or Swiss pattern

Swiss or American?

Square files can be either Swiss or American pattern.

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