This is a matched set (2 each) of professional quality 1-2-3 blocks They are precision ground and case hardened to RC 55-62 on all six sides. They contain no holes. Overall sizes are within +/- 0.0002 inch Flatness and parallelism are within 0.0002inch. Squareness on all sides to within 0.0002 inch. Pairs are matched to a tolerance of 0.0002 inch. There are 2 pieces per set.