The Cylinder Blocks (also called the Knobbed Cylinders) is a classic piece of Montessori material that develops skills in size differentiation. The set consists of four blocks each containing ten cylinders of varying lengths and/or diameters. Each block and cylinder is made of solid beechwood with a natural, satin-touch finish, and each cylinder has a large wooden knob attached for a secure and comfortable grip. The cylinders fit precisely within their spaces, but not so snug that they can't be easily removed and re-inserted. The size of each piece in this set corresponds with a piece from the Knobless Cylinders set (sold separately). The Rack for Cylinder Blocks makes a great storage and display solution, and a Mini Cylinder Blocks set is also available.