Price is per caster. Casters put the HQ Little Foot Frame, HQ Studio or Studio2 Frame, HQ Fusion Frame, HQ Gallery or Gallery2 Frame on wheels so you can easily move the frame. Each frame requires four to eight casters, depending on the length (and number of legs) of the frame. (A caster replaces each leveling foot in the frame.) NOTE: These casters do not fit original HQ Avante or HQ Fusion frames with curved back legs. Sold individually.