What is the difference between a try square, a combination square, a speed square and a framing square?

The squares in a shop wall all promise a right angle, and the differences between them are about size, adjustability and what they physically register against. Choosing wrongly is not dangerous, just slow — most people use a combination square for everything a try square does and never miss it.

Step by step

1. Buy a combination square first.A 300mm one with a hardened blade and a cast head covers 90 degrees, 45 degrees, depth, height and scribing. It is the tool that displaces the most others, and it is the right place to spend money because everything you mark inherits its accuracy.
2. Add a speed square if you cut framing timber.For crosscutting studs, joists and battens, the lipped fence and thick body make a square cut almost automatic with a circular saw. It is a guide first and a marking tool second.
3. Add a framing square for layout.The moment you are setting out on a sheet of plywood, marking a stair string or squaring a large frame, a small square stops being useful because it cannot span far enough.
4. Keep an engineer's square for checking only.Its value is that it is known to be right. Using it as a general marking tool on site is how it stops being right.
5. Test whichever you buy before you trust it.The flip test against a known straight edge takes half a minute and it fails cheap squares regularly. Do it on the day you buy it, while it can still go back.
6. Register the stock properly every time.The stock has to be in hard, full contact with a clean edge. Chips of sawdust, a knock while marking, or a rough sawn edge will all put the line out by more than the tool's own error.

Tips

• The combination square's head slides off, leaving a hardened steel rule — which is a genuinely useful straightedge and depth rule in its own right.
• Most combination square heads have a small spirit vial and a scriber in the handle. Both are convenient and neither is precise; use a real level and a real knife for anything that matters.
• A framing square laid on a board with its two arms touching a circle marks a diameter, which is the quickest way to find the centre of a round object.
• Do not leave a square loose in a toolbag. Every square in this list is only worth having while it is still square.

Alternatives

• Try square: Fixed blade set permanently at 90 degrees in a thick stock, usually 150 to 300mm. Marks and checks square on small joinery work. Simple, cheap and either accurate or not — there is nothing to adjust. Largely superseded for most people by the combination square.
• Combination square: A hardened rule sliding through a head that gives 90 and 45 degrees, with a locking screw. Marks square lines, marks mitres, gauges a depth, sets a height, scribes a line parallel to an edge, and comes apart to give a straightedge. The single most useful marking tool for general work.
• Engineer's square: A precision-ground solid square, usually small, used for checking rather than marking — a saw blade against its table, a planed edge against a face, a machine setup. Made to a tight tolerance and worth protecting from knocks.
• Speed square: A cast triangle with a lipped fence. Its real job is to guide a circular saw or a handsaw for a square or angled crosscut, because the fence hooks over the board edge and the thick body gives the saw shoe something to run against. Also reads roof pitches and common angles.
• Framing or roofing square: A large flat L, typically 600 by 400mm, with no stock. For laying out on sheet material, marking large right angles, setting out stair strings and rafters, and checking big assemblies. Too big and too thin to mark small work accurately.
• Sliding bevel: Not a square at all — a lockable blade that copies any angle rather than holding a fixed one. Used where an angle exists in the building and needs transferring to a workpiece, which is most of the time in an old house.

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