These locking caster wheels are sold as a set of 4. They will fit SWR, Gallien-Kreuger, Ampeg and many more amplifiers. We are the only shop selling these locking casters. This set does not include the socket in which the caster itself, is inserted. This is only a replacement caster set. Usually the caster is the part of the whole caster system that is takes the brunt of the beating and is typically the only part needing to be replaced.