Tetra Tops - Small size (also called Starter) are manufactured by Duncan. Each top is made of acrylic marbles fused together to create basic three dimentional geometric shapes. They're great for kids or adults and have the unique quality of being able to spin on any marble. They claim to be the only top with multiple axis of spin. The top and bottom marbles appear to stand still as the other marbles spin around in a blur. The Tetrahedron has the unique quality of flipping over and spinning upside down. Tetra Tops can also stack on top of one another. This size is perfect for children with small hands. $4.95 is for one small tetra top. Sizes vary slightly, but are roughly 1 inch in diameter (26 mm).