An apparatus comprising an arm with a depending hollow attachment housing, into which is inserted a corresponding attachment portion of a depending device. The housing and attachment portion both have corresponding openings which come into alignment when the attachment portion is inserted into the housing. The apparatus comprises a securing segment which passes through the aligned openings in the housing and attachment portion to prevent the vertical separation of the housing and attachment portion, and a sleeve which surrounds the housing and is vertically moveable between a first position wherein it exposes the openings and securing segment and a second position wherein it covers the securing segment thereby preventing the securing segment from becoming dislodged. The housing comprises a removable delimiter which reduces the allowable vertical movement of the sleeve so that its vertical movement is restricted so as to prevent the sleeve adopting its first position.
