Increased Precision - The 50B trammel head is designed to have an adjustable point for extra accuracy. It is made with cast-iron bodies and designed with spirit level indicators. The blades are also accurate, machine-divided graduations. Reversible Lock Bolt - This feature allows the choice of which graduated side of the blade faces the operator. It will be easier to scribe circles and arcs that are too large to be drawn by using a common divider and compass in the market. Spirit Level Indicator - This feature indicates when the base reference surface is level. This feature is not usually available on comparable protractors in the market. The points also have a 3"/75mm point size. Made To Last - This tool is made with durable materials. The protractor heads are made of cast iron and finished with a black wrinkle finish or smooth black finish. The blades are tempered steel with accurate, machine-divided graduations. The Standard for Excellence - Proudly made in the USA, Starrett combines over 140 years of American heritage and innovation with globally sourced materials to deliver exceptional quality tools and products. The Starrett 50B is a newer version of our old 50A model. Trammel heads are used to measure the distance between points that are too great to be reached with dividers. The heads are die-cast with a black wrinkle finish and have hardened, forged steel divider points. The points screw into the heads, and the pencil socket accompanying each set of trammel heads can be used in place of either point. Includes 2 heads, 2 points, and a pencil socket. This version has an adjustable point for increased precision. The blades are made of machine-divided tempered steel while the heads are made of stable cast iron with a choice of attractive black wrinkle finish or smooth black finish. Cast-iron bodies and through hardened steel divider points. The reversible lock bolt feature allows the choice of which graduated side of the blade faces the operator. It will be much easier to draw arcs and circles that are too large to be drawn by the common compasses and dividers from your local hardware stores. It also has a spirit level indicator that indicates if the base reference surface is level; This feature is not usually common in comparable protractors in the market. The point size is 3"/75mm and it is also made in the U.S.A.