Put the hardwood disc onto the birch plywood rotary disc and spin. Each disc has a different pattern to create a different visual effect in rotation. Children will enjoy their first experiences of physical laws and optical phenomena, as well as using their motor skills to begin the rotation of the discs. 5 Hardwood discs. Rotary Disc: 230 x 15mm (dia. x d). Hardwood Discs: 230mm (dia. ). Suitable for ages 3+.