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A try square is one of the simplest tools in a joinery kit, but small errors show up quickly in timber work. A shoulder that is 1 mm out over 50 mm can leave a visible gap, and a slightly twisted square can make every marking line wrong. For checking small mortises, tenons, housing joints, box joints and frame parts, the best square is not necessarily the biggest or most expensive one.
What Makes a Good Try Square
A try square has a blade fixed at 90 degrees to a stock. The stock bears against the timber edge while the blade checks or marks the face. For joinery, look for a rigid blade, a stock that sits flat without rocking, and a joint between the two that will not shift with ordinary use.
The blade should be straight along both edges. Hold the square against a known straight board and check for gaps by backlighting it. Then test the square itself: place the stock against a straight edge, mark a line, flip the square over from the same edge, and mark again. If the lines diverge, the square is not reliably square. On a small square, a 0.5 mm error is already significant.
Traditional wooden try squares are pleasant to use and easy to read, especially when the stock is made from contrasting woods. Their weakness is movement. Damp storage, changes in temperature and knocks can alter the stock or loosen the blade. A steel or stainless-steel square is usually the safer choice for a site box or workshop that is not climate controlled.
The Best Sizes for Small Joinery
For most small timber joinery, a 4-inch or 6-inch blade is the useful middle ground. A 4-inch square fits neatly inside a cabinet, drawer or small frame and is less likely to catch on nearby edges. A 6-inch version reaches across wider stock and is easier to use for checking the ends of boards.
A 3-inch square is excellent for small boxes, thin stock and marking short shoulders, but its short blade can be limiting on 75 mm or 100 mm timber. An 8-inch square gives better reach but is more awkward around narrow openings. It is also easier to apply sideways pressure and accidentally tip the tool, particularly when checking the inside of a joint.
| Blade size | Best use | Main advantage | Limitation |
|---|---|---|---|
| 3 inch | Boxes, small drawers and thin stock | Fits into tight spaces | Limited reach on wider timber |
| 4 inch | General small joinery | Compact and easy to control | May not span larger faces |
| 6 inch | Frames, cabinets and ordinary bench work | Useful reach without much bulk | Less convenient inside small assemblies |
| 8 inch | Wider boards and larger timber | Checks a greater area in one pass | More prone to tipping and obstruction |
What to Buy
If you want one square for small timber work, choose a 4-inch or 6-inch steel try square with a thick stock and a clearly visible blade. A stainless-steel blade resists rust and is a sensible choice if the tool will live in a tool bag. A hardened blade is less likely to develop a burr along its edge, though even a good square can be damaged if used to lever a joint.
For a small workshop, a traditional 4-inch wooden try square can be entirely adequate. It is often cheaper and comfortable to hold. Check it before buying if possible, and recheck it periodically. A wooden square that has been accurate for years can still move after being stored against a radiator or in a damp shed.
A compact engineer’s square is another option. Its blade and stock are normally machined or ground as a single accurate assembly, so it can be very precise. However, the stock is often shorter and thinner than a woodworking try square. That makes it good for checking small shoulders and tenons, but less comfortable against a rough-sawn timber edge. Search for a 4-inch engineer’s square if precision matters more than a broad woodworking stock.
Checking Joints With a Square
Do not check an unfinished joint only at the end. Check the layout first, then check each component after cutting. With a tenon, place the stock against the reference face and inspect both cheeks and the shoulder. The shoulder should meet the face at 90 degrees, with no daylight at either corner. Check both sides because a shoulder can be square on one face and undercut on the other.
For a mortise, use the square to check the marked ends and the surrounding face, but do not assume the opening tells the whole story. A mortise can look square at its mouth while its bottom is sloping. Check the tenon fit with a thin shim or feeler gauge if necessary. A gap of around 0.2 mm may be acceptable in a dry test fit, but a 1 mm gap at a visible shoulder usually needs correction.
When checking a housing or dado, put the stock against the reference edge and extend the blade across the cut. Check both ends of the housing. If the blade touches one corner and shows a gap at the other, correct the cut with a sharp chisel rather than forcing the mating board into place.
Care and Maintenance
Keep the square in a separate pocket rather than loose with chisels, drill bits or screws. A single nick on the blade edge can create a false gap when marking. Wipe steel blades after handling them and apply a very light corrosion inhibitor if the tool is stored for long periods.
Never use the blade as a scraper, pry bar or screwdriver. If the stock is loose, repair or replace the square; tightening a visible screw may not restore its original alignment. For a second, more robust square in a site kit, a 6-inch stainless-steel try square is usually a better investment than buying a large general-purpose framing square.
A Practical Buying Choice
Choose a 4-inch square for boxes, small cabinets and delicate fitting work. Choose a 6-inch square if you regularly work with 75 mm or wider timber, or want one tool that can check both small joints and cabinet parts. A cheap square is fine when it passes the flip test, stays protected and is used for occasional work. Spend more for a machined or hardened square when you need repeatable accuracy across many joints, work on site, or cannot afford to discover an error after glue-up.