In addition to the Chapter, Council and Commandery, there are other Masonic bodies whose membership is predicated on membership in the Royal Arch or other / all bodies of the York Rite. These are styled "Appendant Bodies."
They are invitational in nature. Candidates must be a member of the York Rite or one of its bodies, be invited by a member of the body, and pass a ballot for membership.
Like most invitiational organizations, members represent the more dedicated and select members of the fraternity. This selectivity is generally expressed in the limitations of the body's membership size, selection processes and requirements.