What is a Combination Square?

Shannon Kietzman
Shannon Kietzman

A combination square is used in woodworking to help achieve the angles necessary to complete the project. It is typically used for framing houses or in small woodworking projects, such as cabinets and dressers. There are several different types of squares available for woodworking, such as the framing square, try square, and precision steel square, but the combination square is the most popular and is generally considered to be the most useful.

In addition to helping the woodworker measure a 90° angle for the pattern being created, the combination square has a 45° shoulder that is used to check and lay out miters. This feature is useful to the woodworker because it eliminates the need to use a separate tool for laying out the miter. This type is more efficient than other types of squares because it is capable of completing two jobs.

A knob located on the rule-type blade is used to reposition the combination square's head. This helps create a tight fit along the desired angle. When purchasing a square, it is essential to choose one that is easy to adjust. Otherwise, the tool can be frustrating and difficult to use.

The combination square also has a scriber, which is housed in the head, and a vial used to determine if the wood is level and plumb. This is useful when creating angles because it ensures they are accurate. Even the slightest inaccuracy can cause the entire project to be flawed. Drawers in small projects may stick or open on their own, doors in houses may not shut properly, and an entire house can look lopsided or crooked if the square is inaccurate or not used properly.

Fortunately, a combination square can easily be tested for accuracy by taping a sheet of paper to a board with a straight edge. It is important for the edge of the board to be perfectly straight. Otherwise, the tool will not be accurate after realignment.

After taping the paper to the board, the combination square should be held against the ledge and a line should be drawn along the outer edge of the blade. Next, the square should be turned over so the opposite side of the blade is facing up. It must then be aligned to the edge of the stock and a second line should be drawn about 1/32 inches (0.079 centimeters) away from the first. If the combination square is accurate, these lines will be perfectly parallel.

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Discussion Comments


@DentalFloss, while I know many people feel intimidated by math and measuring, I do think you can figure it out. The next time you need to use something like a combination square, just ask someone else to help you figure it out, you might get it right next time.


@hyrax53, I have to agree with you. I struggled so much with anything like that- wood shop in middle school, geometry and other visual math in high school...some people just cannot visualize things in that way, I think. Admittedly, this might sound ridiculous to other people who are good at these things, but I do think some people are just more naturally equipped for these things.


When I was had to take woodworking in school, I tried desperately to understand how to use the tools, including the combination square sets. Unfortunately, I could never quite grasp the way to visualize angles and lines in order to cut things out properly. I honestly think that using tools like combination squares, protractors, and all of those other angle measuring tools is at least a little bit genetic. Yes, I can use a ruler, but anything more complicated and I just can't do it.

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