There’s a tool in almost every woodworker’s apron that never gets the attention it deserves. It has no battery, no motor, no display, and no moving parts worth mentioning. It’s a try square — a flat blade fixed at exactly ninety degrees to a thicker stock — and it quietly decides whether your joints close up tight or leave gaps you spend the rest of the project trying to hide.
Most beginners buy one, use it a handful of times, and then reach for a combination square or a speed square instead, because those look more versatile. That’s a fair instinct, but it skips the point: a try square does one job, and it does it with a level of honesty that adjustable tools can’t always match. Once you know how to use it properly — and how to check that it’s actually square — it becomes the tool you reach for every time accuracy matters.
What a Try Square Actually Is
A try square has two parts. The stock is the short, thick handle, usually wood, plastic, or metal. The blade is the longer, thinner arm, usually steel, fixed rigidly at ninety degrees to the stock. The inside edge of the blade and the face of the stock form the working reference: when the stock sits flat against the edge of a board, the blade lies across the face at a true right angle.
The word “try” here doesn’t mean “attempt.” It comes from the old workshop sense of trying, or testing, a piece of work — checking it against a standard. That’s exactly what the tool is for: testing whether an edge is square, and marking lines that are square to an edge.
Try squares come in a few sizes. A 6-inch blade suits small boxes and joinery. A 9-inch or 12-inch blade handles furniture parts and sheet goods. Bigger isn’t automatically better — a long blade on a small workpiece is awkward, and a short blade on a wide board won’t reach across. If you buy only one, a 9-inch model covers most general work.
How to Check Whether Your Try Square Is Square
This is the step most people skip, and it’s the one that matters most. A try square that is out by even a fraction of a degree will pass that error into every line you mark with it. Fortunately, checking it takes about thirty seconds and needs nothing but a board with one straight edge.
Hold the stock firmly against the straight edge of the board and draw a line along the blade. Then flip the square over — stock against the same edge, blade pointing the other way — and draw a second line from the same starting point. If the two lines sit exactly on top of each other, your square is true. If they diverge into a V shape, the square is out, and the gap between the lines is twice the error.
A cheap square that fails this test is not worth keeping for joinery. You can sometimes true up a wooden-stocked square by carefully filing or sanding the blade seat, but for most people the honest answer is simpler: replace it. Accuracy is the whole product here, and a square you can’t trust is worse than no square at all, because it gives you false confidence.
Repeat this test every few months, and any time a square has been dropped on a concrete floor. Squares don’t announce when they go out of true; they just quietly start lying to you.
Marking a Square Line Across a Board
This is the try square’s bread-and-butter job, and doing it well comes down to registration. Place the stock flat against the reference edge of the board — the edge you trust, usually the one you jointed or the factory edge — and press it firmly so there’s no gap and no rocking. The blade should lie flat on the face of the board. Hold a sharp pencil or, better, a marking knife against the blade and draw the line in one smooth pass.
Two details make a real difference. First, mark from the reference edge, not from a random edge: every measurement in a project should trace back to the same trusted faces, or small errors stack up. Second, use a knife rather than a thick pencil for joinery lines. A knife line is thinner, more precise, and it gives your saw or chisel a tiny groove to start in, which keeps the cut from wandering.
If the line needs to wrap around the board — for a cut that has to be square on all four sides — mark one face, then carry the line around the edges with the square registered against the same reference face. Check that the lines meet where they should. If they don’t, something is off: either the board isn’t square, or your registration slipped.
Checking a Board or Joint for Square
Marking lines is only half the job. The other half is testing work you’ve already done. After gluing up a frame or a box, press the stock against one inside edge and look at the blade against the adjoining edge. Any gap between the blade and the wood, even a hairline, tells you the corner isn’t square. Check all four corners, not just one — a frame can look fine at one corner and be out at the opposite one.
This check is just as useful before assembly. When you’ve cut the parts for a cabinet carcass, test each board’s ends for square before you glue anything. Catching a board that’s a degree out at this stage costs you a minute of re-trimming. Catching it after glue-up costs you a project.
One caution: a try square checks a corner at the point where you hold it. A long board can be square at one end and bowed in the middle. For checking the overall squareness of a large assembly, pair the try square with the diagonal test — measure both diagonals of a frame, and if they match, the frame is square regardless of what any single corner seems to say.
Try Square vs Combination Square vs Speed Square
These three tools overlap, and the overlap causes confusion. Here’s the practical split.
A combination square has a sliding, adjustable head. That makes it versatile — it marks 45-degree angles, measures depth, and works as a height gauge — but every adjustment is a chance for the setting to slip, and the head can wear out of true over time. A try square has no adjustment to slip. For a pure 90-degree check, it’s the more trustworthy tool.
A speed square is built for speed on construction lumber: marking rafters, guiding a circular saw, finding angles fast. It’s excellent on a job site and less suited to fine joinery, where its thick body and stamped markings are coarser than a try square’s machined edge.
None of this makes the other tools useless. It means each has a lane. When the question is simply “is this square, exactly?” — the try square is the answer. Keep the combination square for the jobs that need its adjustments, and the speed square for framing.
Common Mistakes That Ruin Accuracy
The first is registering against the wrong edge. If you mark from a rough-sawn or bowed edge, the line will be square to that bad edge and wrong everywhere else. Always work from your best, straightest edge, and mark it so you know which one it is.
The second is letting the stock rock. If sawdust or a splinter gets under the stock, or if you press harder on one end than the other, the blade lifts and the line drifts. Brush the edge clean and press the stock flat along its full length before marking.
The third is trusting a square you’ve never tested. Test it when you buy it, test it after a drop, and test it a couple of times a year. The test takes half a minute and it’s the difference between a tool and a paperweight.
The fourth is using a dull pencil. A thick, soft pencil line can be a millimetre wide, which means your “precise” line is actually a zone. Sharpen the pencil to a fine point, or use a marking knife for the lines that matter.
Caring for a Try Square
A try square asks for almost nothing. Keep it dry — a steel blade left damp will rust, and rust on the working edge ruins accuracy. Wipe the blade with a lightly oiled rag every now and then, especially in a humid shop. Don’t use it as a hammer, a pry bar, or a straightedge for a utility knife; cutting against the blade nicks the edge and a nicked edge can’t register cleanly. Store it where it won’t get knocked around, hanging on the wall or in a drawer with a bit of protection, rather than loose in a toolbox with chisels and wrenches.
If the stock is wood, a coat of paste wax now and then keeps it smooth and resistant to moisture. If it’s a budget model with a plastic stock, check the blade joint occasionally — that’s where cheap squares tend to loosen first.
Frequently Asked Questions
Can I use a try square to mark 45-degree angles? No. A try square only gives you 90 degrees. For 45s, use a combination square, a mitre square, or a speed square.
Is an expensive try square worth it? Up to a point. A mid-priced machined square from a reputable maker is noticeably more accurate and durable than the cheapest option. Beyond that, you’re paying for fit and finish more than accuracy. The test described above matters more than the price tag: a cheap square that passes is better than an expensive one that doesn’t.
Can I use a try square on metal? Yes, for marking and checking, though the blade will wear faster than on wood, and a dedicated engineer’s square is the better choice for metalwork. Keep your woodworking square for wood if you can.
What size should I buy first? A 9-inch blade is the best all-rounder for furniture and general workshop work. Add a 6-inch model later if you do a lot of small boxes or detailed joinery.
The Bottom Line
The try square is not a glamorous tool, and that’s precisely why it gets overlooked. But nearly every square joint in a project — every cabinet that sits flat, every drawer that slides without binding, every frame that doesn’t rack — traces back to somebody checking and marking with a tool like this. Buy one that’s actually square, test it regularly, register it against a trusted edge, and mark with a sharp line. Do that, and the most boring tool in your shop quietly becomes one of the most important.
