The Starrett C434-18-16R Combination Set has a square head, center head, reversible protractor head, and 18" blade with 16R graduations (1/32", 1/64", 1/50", and 1/100"). The protractor head is cast iron with a satin chrome finish on the reading surface and black enamel finish elsewhere. It has revolving turrets with direct-reading double graduations of 0 to 180° in opposite directions, for accurate reading of angles above or below the blade. It is reversible, with shoulders on both the front and back for reading on both sides.

The blade is made of hardened steel with a satin chrome finish, and the square and center heads are forged, hardened steel with a smooth black enamel finish. The square head has a scriber, a 90° square face, and a 45° miter face. It can be used for scribing right angles and parallel lines, or as a tri-square, miter, depth gauge, height gauge, or level. The center head accurately locates the center of cylindrical or square work. All heads have reversible bolt locks, and the square head and protractor head each have a spirit level. The combination set comes in a protective case.

Protractors are tools that measure specific angles, which allow users to create and replicate desired angles. The tools include a stationary base and movable rule, usually connected by a scale that may be digital or manual. They are useful in a wide range of applications, such as measuring crown molding and installing baseboards. A protractor can be included as part of a combination set, along with a center and a square. A center accurately locates the center of a circle or cylindrical rod. A square is used to scribe right angles and parallel lines, calibrate miter and table saws, or as a miter, height gauge, or depth gauge.

The L.S. Starrett Company manufactures precision measuring tools, metrology and testing equipment, and saw blade products. The company, founded in 1880, is headquartered in Athol, MA.