Steel block sets for adjusting the highest precision measuring instruments.Features & Benefits:-Each gauge block is marked with an identification number-Gauge block sets are placed in their wooden storage box immediately after calibration-Made of high quality alloy steel, carefully heat treated and stress relieved for high stability and precision lapped for good wringing properties. Slightly rounded edges-Range 1.0005mm, 1.001-1.009mm by 0.001 step, 1.01-1.49mm by 0.01 step, 0.5-9.5mm by 0.5 step, 10-100 mm by 10 step