One Pair 2 4 6 Precision Blocks 23 Holes Set of 2 PCS 2 PC 2-4-6 Metal Blocks With 23 Holes ; Flatness within .0002" and parallelism within .0003" Has 23 holes with 5 holes tap to 5/8"-11 threads for clamping and 18 untapped holes Squareness on all sides is 0.0003" per inch. Pairs are matched to a tolerance of 0.0002" Size within +/- .0001" ; Blocks overall dimension while laying down (same size): 4''L x 6''W x 2''H Quantity:2PCS;Unit weight: 18 lbs ; Heat treat and hardness 56 to 60 RC