The Fowler 52-666-777-0 is a 12 piece Angle Block Set for comparing and setting angles quickly and easily. Each block is accurate to ± 30 seconds of arc. Precision ground and hardened. Blocks = 1/4˚, 1/2˚, 1˚, 2˚, 3˚, 4˚, 5˚, 10˚, 15˚, 20˚, 25˚ and 30˚. Supplied in a shop hardened fitted case. Fowler, an American company, manufactures inspection and measurement instruments such as electronic indicators, calipers, bore gages and digital scales. The company founded in 1946, is headquartered in Newton, MA.