Shoes come in four (4) thicknesses and simply click together using powerful magnets in whatever combination is required to provide your required lift height. Shoes can also be screwed to the base of the PT21 Tester for additional security. Included: 2 x 10mm Shoes 2 x 20mm Shoes 2 x 30mm Shoes 2 x 50mm Shoes 4 x M16 Stainless Cap Screws Note: PT21 Tester and other accessories not included