Abstract: A modular workpiece holding apparatus for locating and holding a workpiece in a predetermined position. The apparatus includes a base having a plurality of external faces, each with a plurality of bores arranged in an X-Y grid pattern of parallel rows, the bores alternating vertically and horizontally between first and second different diameter bores. A riser is mounted at a predetermined position on the base by bushings and fasteners extending between the riser and the bores in the base. The bushings in each riser are arranged in diagonally opposed pairs such that one pair of bushings engages the first diameter bores in the base; while the second opposed pair of bushings engages the second enlarged diameter bores in the base. A workpiece attachment member is mounted on the mounting head end of each riser to locate and hold a workpiece. The mounting head of each riser is axially in line with the riser mounting base or offset from the riser mounting base.