Set includes a matched pair of 1-inch x 2-inch x 3-inch blocks, five plated 5/16-18 threaded socket head cap screws, and a hex key wrench. Each block is precision ground and case hardened on all six surfaces. Surface finish is 6 to 16 micro-inches. Squareness on all sides to 0.0001 inch. There are a total of 11 holes on three faces: five 5/16-18 tapped (arranged for holding down and for conversion to an angle plate) and six untapped drilled-through holes with deep recesses for easy clamping. Blocks are over-sized to allow for normal lapping to 0.0003 inches.