The Best Combination Square | Reviews by Wirecutter
12-inch models are the most useful. A combo square with a 12-inch ruler can extend a square line a little over 10½ inches, which is enough for most common widths of lumber (for lengths beyond that, you can flip the square to the other side of the board and complete the line). 16-inch rulers are unwieldy, and 6-inch models are too small.
For around-the-house use, a combo square with a zinc body is the best option. It’s reliable and easy to calibrate, and if the ruler bends, replacing it doesn’t break the bank. In contrast, high-end models like the Starrett have cast iron bodies and tempered-steel rulers, making them premium products with laser accuracy, but at over $100, their cost is excessive for home use.
A stainless-steel blade is important. Regular steel blades will rust to the point where the markings become impossible to read. Some models have a coated blade to prevent corrosion, but once the coating chips off, the blade is toast. Getting a stainless ruler is worth the $5 or $6 upgrade.
For our tests, we came down to six finalists, all but one with a zinc body and a stainless-steel ruler. The oddball was the Swanson TC131 with its plastic composite body. We wanted to see how it would stack up against models with durable metal. We chose tools based on the manufacturer’s reputation as well as on the customer feedback at retailers like Amazon, Home Depot, and Lowe’s. I’m familiar with all of the companies represented, and all are known for quality hand tools.
To test our selection of combo squares, we first confirmed whether they provide a perfect 90-degree angle, and we did any necessary calibrations to correct them. We then used each one during a large garage shelving project, paying attention to overall handling (how easily the ruler slides, the action on the knurled knob, and the ease of flipping the ruler in the base). I also checked each metal ruler for accuracy with an older version of a Lixer Tape Measure Calibration Tool (all of them were well within 1/64 inch of accurate).
