The bolts are graded in diameter for a more difficult exercise. Five slotted bolts and 3½" Stubby Screwdriver. Designed by a Montessori teacher to aid the development of eye-hand coordination and teach a practical skill. The board has separate compartments to hold the driver and the bolts, after the child has removed them. The bolts screw into a long-lasting metal sleeve that prevents stripping. Boards measure 10½" x 4" x 1¼" high. Driver may vary. Ages 3 and up.