8 Piece 1-2-3 Precision 23 Hole Block Set with Socket Screws and a Hex Key Sold in a matched pair. Hardened and precision ground on all 6 sides of each block. Accuracy with squareness on all sides within .0001 per inch. 23 holes consist of 5 tapped holes that are 3/8"-16 thread for clamping and 18 untapped holes. Supplied with a fitted case. Set includes a matched pair of 1-2-3 blocks with 23 holes, 5 pieces of 3/8 -16 socket screws, and a hex key. Shipping Weight: 4 lbs.