[Packing]: 81 Pieces. 9 blocks: .1001-.1009" in .0001" steps; 49 Blocks: .101-.149" in .001" Steps, 19 Blocks: .050-.950" in .050 steps, 4 Blocks: 1-4" in 1" steps [Material]: Set made of fully seasoned alloy tool steel with hardened to 65 RC to provide both long wear and resistance to stains and rust [Instructions]: Blocks manufactured under carefully controlled conditions, allowing for the highest degree of accuracy when used at room temperatures of 68 degrees F (20 degrees C) [Grade]: All gage block sets are certified by an accredited ISO-17025 Gage lab with long form certification. Individual serial numbers on each block, regardless of grade [Application]: Gage blocks are commonly used to calibrate fixtures and precision instruments in workshop, inspection, and dimensional metrology applications, to inspect tools such as mounting tools, cutters, fixtures, and mechanical parts, and in the gage manufacturing process itself. Grade B gage blocks are commonly used in workshops for calibrating and inspecting mounting tools and cutters