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Used to check and mark right angles, squares are defined as steel, try and combination. Combination squares will also measure 45 degree angles. If it has a degree scale, it can determine any angle.

A steel square is made from one piece of steel, with the long end (body) usually 24″ and the short end (tongue) 16″. Similar squares are available in other sizes (9″ x 12″) and other materials (aluminum).

Squares may also have tables or scales, the most common being rafter and Ease tables. These provide information on how much lumber will be needed on a job, as well as information for roof framing.

A try square is used as a guide for pencil markings of cuts and to check the edges and ends of boards to see if they are square. It is also used to determine whether a board is the same depth for its entire length. Try squares have wood, plastic or metal handles.

A combination square combines the best features of the steel and try squares. It has a grooved blade and head that can be adjusted to many locations on the 12″ blade to provide different measurements. The head usually contains one or two levels and a scratch awl for marking. One edge of the handle has a 45° angle for use as a miter square. Some combination square sets are available with an attached protractor that is movable throughout 180º for setting the blade at any angle within that range. Combination square heads (handles) are commonly plastic or metal.

Clarity and legibility of graduations is a key factor in choosing any type of square. Modern techniques enable manufacturers to etch graduations into the blade and create high-visibility markings that are durable as well.


Rafter tables, which appear on steel squares, are used to figure lengths and cuts of rafters. The table consists of six lines of figures, with each line’s use indicated on the left end of the square. The first line of figures gives lengths of common rafters per foot run; second line, lengths of hip and valley rafters; third line, length of first jack rafter and differences in length of the others centered at 16″; fourth line, length of the first jack rafter and differences in length of others centered at 24″; fifth line, side cuts of jack rafters; and sixth line, side cuts of hip and valley rafters. Metric rafter squares are also available.


The Essex Board Measure table, which also appears on steel squares, shows board measure of almost all sizes of boards and timbers.

Inch graduations along the outer edge of the square are used in combination with the values given along seven parallel lines of the table.

The figure 12 on the outer edge represents a 1′ board 12″ wide and is the starting point for all calculations. All inch graduations on both sides of the figure 12 represent board widths, and figures in vertical columns under the inch graduations denote board measure.

To find the number of board feet in a piece of lumber, start under the mark 12 on the outer edge of the square and find the length of the piece. Along the same scale of inch graduations locate the width of the timber. Then follow the line on which the length is stamped toward the column of figures under the width. The figure at the point of intersection indicates board measure of the piece. Figures in the Essex table are for boards 1′ thick. To obtain the measure for any other thickness, multiply the figure given in the table by the thickness of the piece.


Extension rules are used to measure closed-in areas such as doorways and window frames where a regular folding rule will not work. Extension rules feature a 6″ sliding rule in the first section that can be pulled out to measure distances of less than 6″ without moving and marking.


Folding rules usually consist of 6″ to 8″ hardwood lengths connected by spring joints, but are available in steel and aluminum as well. Some have special plastic or epoxy coverings to protect the blade and printed numbers. Better models are painted with clear protective coatings over sharp multicolor printing and highlight commonly used markings for easy reading. Two basic rule styles are inside read and two way.

An inside-read rule is marked on one edge of the blade so that measurements can be read from inside a window or door frame, etc. When the first section of the rule is unfolded, it enables the user to make accurate measurements without removing it from the surface being measured. It is also popular because it always lies flat on the work surface.

The two-way, flat-reading rule is calibrated so that it can be read from left to right at either end of the rule, regardless of which end is unfolded first.

Folding rules are available for specialized uses such as engineering, plumbing, masonry and mechanics. These differ from general use rules in the markings on the rule face.


tape rule is a concave, spring-steel blade ranging from 1/4″ to 1″ wide and from 3′ to 33′ long, coiled inside a carrying case. Metric tape rules come in comparable widths and lengths up to 10 meters.

Because the tape rule is flexible, it provides an easy means for accurately measuring curved surfaces. The concave cross section allows it to be extended unsupported. Contained in the housing of some models are spring mechanisms that release or retract the tape.

Quality features include wider blades, Mylar® or epoxy coating to protect the finish, better cases and return mechanisms. Some include a spring clip for attachment to a belt. Many tapes have markings for laying out studs on 16″ centers or other specialized markings.

Since blades receive hard wear, replacement blades or complete drop-in cartridge assemblies are offered to fit all sizes of tape rules.

In addition to pocket or power tapes, 25′, 50′ and 100′ flat steel tapes are available, as are metric tapes up to 50 meters. Longer tapes are contained in durable cases and rewound by a crank on the side of the case. Continuous filament fiberglass and woven tapes also are available in sizes up to 300′.


This group of tools contains such items as calipers, dividers, micrometers and thread-pitch gauges. These items are used primarily by professionals, but are gaining popularity with hobbyists.

Calipers and dividers are used for transferring measurements from a model to a part being produced. They can also be used to measure holes or objects that cannot be reached easily with a graduated measuring device.

Dial calipers and micrometers are used for close-tolerance work using drill presses and lathes. These devices can make inside, outside and depth measurements to within .001″.

Thread-pitch gauges are used to determine the exact thread pitch needed for replacing screws and nuts.

Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.