80 shown in fig7 the plate 70 includes a vertical slot 82 that is open at its upper end to engage the hub 84 of the freely rotating wheel assembly 80 the wheel assembly 80 see fig8 includes a shaft 86 in the hub 84 that extends through the slot 82 and carries a split hanger 88 having two sides 82 a and 82 b that engage the inside and outside faces of the plate 70 the rim 90 of the wheel assembly has an inner track 92 large enough to receive a small animal such as a hamster occupying the cage when the animal runs on the track the wheel rotates enabling the animal to run substantially in place the top portion 94 of plate 70 cooperates with a rib 98 adjacent the upper edge of the wall 96 of the upper section of the support to hold the upper section in place the upper and lower sections 42 and 44 of the support 40 may be separated simply by squeezing the side walls 46 and 48 together so as to disengage the posts 66 and holes 68 the support 40 is also preferably made of abs nylon lexam or other plastic material which is chew resistant the wheel assembly may be mounted in other ways on its support but it is particularly advantageous to have it mounted on a plastic support rather than a wire or metal support as the assembly generates little or no noise in accordance with other embodiments of the invention the support 40 may be formed in many different shapes and may either be a unitized or multi component construction and the wheel assembly may be mounted on the support in a variety.