BL-123 Pair of 1″ x 2″ x 3″ Precision Steel 1-2-3 Blocks Review Posted on November 24, 2018 By DaughterSeaUrchinTagged 1 2 3 Blocks, Hardware, Pulls, Tools & Home Improvement Heat treated above 48 Rockwell “C”; .0001 to .0003 over allowance for nominal lapping. Squareness of all sides is within .0002 per inch.