Anytime Tools 2-4-6 Blocks Matched Pair Hardened Steel 23 Holes (2"x4"x6") 246 Set Precision Machinist Milling MATCHED PAIR, Professional Quality Tool Precision ground Steel and Case Hardened on all six sides Squareness on all sides within 0.0003" Surface finish from 6 to 16 microinches 23 through holes (5 tapped 5/8"-11 TPI and 18 plain)