HHIP Dasqua Ultra Precision 23 Hole 1-2-3 Block Set. Squareness is 0.0001"/1". Heat treated and case hardened to HRC 58-62. Hardened and precision ground on all 6 sides of each block. Tolerance of size +/- 0.0002". Parallelism 0.0002". Height of pair 0.0002". Cross drilling design gives minimum weight and maximum strength. Supplied in a durable fitted ABS case.