# What is a folding rule?

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Folding rules, sometimes called zig-zag rules or jointed rules, are a series of two or more smaller rule strips joined with hinges. These rules can be folded together to be carried easily, or used in confined spaces. They can also be folded out and used to measure longer distances or take measurements that are further away and difficult to reach.

These rules are often divided into 150 mm (6″), 200 mm (8″) or 250 mm (10″) sections. They are typically marked with either metric or imperial measurements or both. Some folding rules also have other markings, depending on their intended use.
Folding rules can be made from different materials, such as steel, aluminium, fibreglass, plastic or wood. The rule strips are joined with hinges and each strip can be folded against each other to keep it short. Once the strips are opened out they can usually be fixed into place, which creates a long rigid rule.

## Uses

### Measurement

Folding rules can be used for measuring both small spaces and longer distances. They can be transported easily once they are folded up, making them useful when working in the field.

Folding rules can also be used to measure a point which is difficult to reach. They can be extended out to form long, rigid pieces which can reach across or up without bending very much. Some folding rules can be extended to up to 3000 mm (120″) long, depending on individual rules.

### Angles

Folding rules can also be used to help determine angles on larger structures or for places which are difficult to measure with a just protractor. Sections of the rule can be lined up with an angle, the angles of the rule can then be measured with a protractor.

For more information see:  How to measure angles with a folding rule

### Parallel lines

Folding rules with more than two rule strips can be folded in such a way that it can be used to quickly draw parallel lines down a surface with a straight edge. These rules can be folded into a the shape of a ‘4’ held upside down with two rule strips at right angles to each other. One rule will line up with the edge of the surface and it can be moved up and down to draw parallel lines.

### Special marks

Some folding rules come with specialist markings, for different uses. For example, masonry folding rules have markings on one side to show the proper dimensions of the bricks and mortar joints needed to lay a structure of a specific height or length. Surveyor’s folding rules are distinctly marked out every 10th of a foot or metre.

## Folding rule or tape measure?

Folding rules are considered to be predecessors of modern tape measures, which are long flexible strips with measurements marked on them which are coiled inside a case. They can be extended out or retracted into a coil inside the case.

The tape measure has replaced the folding rule for many uses. However, the latter still maintains its position for some purposes, such as construction, where rigid long measuring instruments may be preferred over flexible ones.