A lever turning as a whole unit in the bore, rather than just the handle pivoting, usually means the anti-rotation plate is missing, deformed, or was never engaged in the prep. The N523-055 is the ND Series plate for that condition. Pull the outside rose, check whether the plate tabs are still engaged in the door, and replace the plate if they've sheared. If the bore itself has been chewed out oversize, a new plate alone won't hold.

It's the anti-rotation plate for Schlage's ND Series heavy duty cylindrical locks. The plate sits between the lock rose and the door face and keys into the door prep so the outside trim cannot spin in the bore under abuse or heavy lever use. It's a replacement part, not a complete lock, so it only helps if the rest of your ND lock is already in the door.

Just a part. The N523-055 is a single anti-rotation plate, ordered by model number on its own, with no lever, rose, cylinder, or latch included. If a lever is loose or spinning on an ND lock, this is the piece that stops the rotation, but you order the lever, chassis, or latch separately if those are also damaged.

If the openings are all ND Series cylindrical locks, the N523-055 is the one plate part number to stock for that condition, which makes it a reasonable line item to keep on the MRO shelf for a facility standardized on ND. Buildings with a mix of ND and other Schlage lines will need the plate that matches each line.

The plate is offered as a single model, N523-055, with no finish or size options to pick. It's a concealed part that sits behind the rose, so finish isn't a selection you make here the way you would on a lever or escutcheon.