Try and mitre squares are marking and checking tools used to assess angles and mark straight cuts. They consist of two straight pieces, the stock and the blade, which intersect one other at either 90° or 45°.
A try square is used for checking right angles (90°) and a mitre square is for 45° angles (135° angles are also found on mitre squares because they are created by the 45° intercept).The pieces of the try square intercept at the end, giving the tool the appearance of a right angle triangle, minus the hypotenuse or a capital L. One of the mitre square pieces joins to the centre of the other, making it look like a wonky T.
However, there are squares available for both 45° and 90° angles which are known as either try squares or try and mitre squares. These are different to combination squares which look similar and also measure 90°and 45° angles. The difference is that the two parts of a combination square are detachable and adjustable and include the two angles on either side of a single handle piece.
There are also try and mitre squares which are capable of measuring other angles. These squares are adjustable and pivot around the joint, to the desired angle size.
The “try” in ‘try square’ refers to the testing (trying) of a surface for straightness and its relation to adjoining surfaces. It is however, occasionally written “tri”, as in triangle, the prefix referring to three. This could be due to the triangular shape, but is the incorrect term.
A mitre is a type of joint, which sees two bevelled pieces coming together to form a corner. The most common mitre joints make 90° corners and consist of two 45° bevels. Mitre squares can therefore be used to create mitre joints.
A square is another name for a right angle, but is often the name given to the tools which measure various angles. These include combinations squares, folding squares, combi squares and roofing squares.