Made of Quality Alloy Tool Steel Grade EN31 instead of Mild Steel. Read material characteristics of EN31 & its advantages over Mild Steel in description below. Size of the block is 1" x 2" x 3". Total 23 Through Holes being done in 1 operation (5 tapped drills 3/8" x 16 TPI & 18 plain drills) .Drilling & Tapping done on computer controlled Vertical milling center to avoid sloppiness & misalignment. The squareness and parallelism is controlled well within 2-3 microns. Deep Hardened , Matched Pair, Precision Ground , Even Chamferring on all 6 sides. These matched pair can be bolted through any plain hole to the tapped hole to use as a Steps blocks, feelers, Jigs, Angle plate, orientation and setting up tool.