A combination square is a versatile adjustable measuring tool that quickly and accurately measures objects for precise work. A combination square is an essential tool for any toolbox, more used for meticulous work than production work. This hand tool comes in various sizes ranging from small ones you can keep in your pocket to larger heavy-duty ones that come with all the attachments for bigger jobs.The construction of a Combination SquareSquare head (also known as a mitre head or an anvil) – has a slot which the rule fits through which is locked in place by a screw. Made from die-cast alloy, aluminium, cast iron (strong and resistant to oils and chemicals). More expensive ones are made of forged and hardened steel.Rule or blade – manufactured from steel or hardened and tempered steel, accurate markings (metric and imperial) etched into the steel rules, thicker steel blades are better.Level bubble vial – acts as a spirit level.Protractor head – used to set and mark angles.Centre Finder – easily indicates the centre of a round object.Scriber to mark lines – usually inserted in the end. The heads need changing in order to use the other devices. They are precision instruments which need to be stored carefully as damage to the tool can cause inaccuracies. What are Combination Squares are used for?Measuring straight lines perpendicular to an edge.Measuring 90 degree and 45-degree angles, drawing lines parallel to the edge, easy to layout a triangularAdjustable depth for repetition marking and scribingMarking a line around a post or bean for cuttingFind centre of a round object, for example, dial or rodMeasuring the depth of a grooveDetermining flatnessSetting bits and blades, for example, the height of bladeUse the rule/blade on its own as a ruler Fine-tune a machineProjector heads – finds any angles you requireSome have to spirit levels on the tool ideal for small jobs