The invention comprises a rigid frame that is positioned around the skull to define a multi-dimensional coordinate system. Multiple arms are coupled to the frame, each arm having an attachment assembly movable along a longitudinal axis directed toward the center of the rigid frame assembly. Multiple receptors are either attached to the skull or drilled into the skull for receiving an associated attachment assembly. The receptors provide a mounting base upon which the frame is repeatedly attached and detached from the skull at the same reproducible reference location. Each arm has a multi-station receptacle that receives various attachments used for mounting and attaching the receptors. Special bushing are used to lock the attachment assembly in a preset longitudinal position in relation to the arm. The locked attachment assembly can then be removed from the arm allowing the frame to be removed from the skull while maintaining frame position information.