Machinist Squares Set Features include... Manufactured to workshop grade specifications. Hardened spring steel blades are permanently secured to beam to ensure rigidity. Precision ground for straightness and parallelism. Working edges of blades lapped to accuracy. Blade length measured from inner edge of beam to end of blade. Set includes the following... Linear Blade Linear Beam Square Accuracy Parallel Accuracy 4" 3" 0.0012" 0.0006" 6" 4" 0.0014" 0.0007" 9" 5.5" 0.0017" 0.0009" 12" 7.5" 0.0020" 0.0010"