Interfaces between nosings on respective frames and frame combinations to be joined. Each nosing has an elongate receptacle extending along the nosing length. A remote wall of the receptacle is displaced from the remainder of the nosing. The remote wall on the nosings to be joined can be generally aligned with and proximate the receptacle opening on the other nosing. With the remote walls and respective receptacles aligned, the frames are moved toward each other with the remote walls on the respective nosings entering the receptacles, with the remote walls in generally facing relationship with each other. Spacings and tolerances of the remote walls, and corresponding receptacles, can optionally provide frictionally-restrained engagements of the remote walls in the receptacles, whereby the frames can be re-oriented with limited assembly support to such assembly without disengagement of the nosings from each other by the action of gravity.