HP Steam Chest stud drilling 1″ & 7/8″ BSF, 1 set of 12 off 7/8″ BSF on 14.1/4″ pcd, two sets of 12 1″ BSF on 14.1/4″ pcd, three sets of six 1″ BSF 9two rows of three 11″ crs, 3.7/8″ crs along row