This is a modular tool rack. Depending on your specific requirements, you can choose from 4 different horizontal shelves:

4141 Balls Shelf (medicine ball shelf)
4142 Angled Shelf (rubberized inclined dumbbell shelf)
4143 Flat Shelf (universal rubberised shelf; e.g. kettlebell holder)
4144 Bumpers Shelf (bumper disc shelf)

Shelves must be supported by columns:

4140 Upright Column Kit.
4139 Mini Upright Column Kit

Two kits are required to compose the basic single-bay shelving unit, which can then be extended by adding other kits. The kits are sold individually so that 2, 3, 4 and 5-bay shelving units can be assembled as desired.

For example, to build a 5-bay racking system, like the one shown in the picture above, you need 6 Upright Column Kit.