Parallels are metal rectangular blocks that are utilized to keep items level when secured in a milling vise, for precision machining or drilling work. Also used in machining, 123 blocks are blocks of steel that are precisely squared and parallel, and measures 1 inch thick x 2 inches wide x 3 inches long. These blocks are used primarily in inspection setup tasks. A machinist straight edge is used to measure flatness. These rigid bars have precision machined edges for making and cutting straight lines.