Square Head and Steel Rule
The square head and rule is employed to layout lines parallel and at right angles to an edge. It may be utilized as a depth gauge or for checking 45° and 90° angles. The square head can be moved together with the ruler to any position.
Steel rule is utilized as a straight edge or for measuring. It may be fitted to the center head, bevel protractor or to the square head. Metric combination steel rulers are usually graduated in 1 mm and 1/2 mm whereas imperial combination set rules are usually graduated in inch that is 8th or 16th on one side and 32nd and 64th on another side.