The Starrett 135A pocket level is a 2-1/2" long spirit level with a single vial for determining horizontal plane and smooth, convex ends for fitting in a pocket. The vial is made of glass to resist scratching and provide clear readings, and has a sensitivity of 17 to 21 minutes. The level has a hexagonal brass body with a satin nickel-plated finish that resists corrosion. Levels are used in the building trades, engineering, surveying, and metalworking, among other applications.
Levels are instruments that are used to determine the true horizontal or vertical plane of a surface. The most common type of level is the spirit level, or bubble level. Spirit levels have a liquid-filled, bowed tube (also called a vial) with a bubble that moves when slight adjustments are made to the level. When the bubble settles between marked points on the vial, it indicates that a surface is horizontally or vertically straight. Levels can have one or more vials to determine the horizontal plane, the vertical plane, or various points between, such as a 45-degree angle, simultaneously. Some levels include a laser line indicator that projects a horizontal or vertical beam on a surface. Bullseye levels, or surface levels, are circular, flat-bottomed spirit levels that determine whether a surface plane is level. Machinists’ levels are made of metal and have surfaces designed specifically for rugged use in a machine shop or tool room. Levels can range from highly-complex and accurate machines, such as those used in the surveying and construction industry, to precision instruments used in carpentry and other building trades, to simple, pocket-sized devices for do-it-yourself projects.
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.