The Schlage N523-221 is the OEM spring cage and lever catch assembly for the ND Series cylindrical lock, specifically for locks manufactured after January 31, 2017, in the interior less-cylinder position. It is documented in both the Schlage ND Series Service Manual (document 111524 - the post-January 2017 manual) and the Schlage NDE Series Service Manual (document 015478) as the universal inside spring cage for all ND functions.
The alternate part number for the N523-221 is 168608. Both numbers reference the same assembly.
What the Spring Cage and Lever Catch Assembly Does
The spring cage is the housing that contains the torsion spring for the inside lever on the ND Series trim. When the inside lever is pressed down to retract the latch bolt, the spring inside the cage compresses under the lever rotation. When the lever is released, the compressed spring drives the lever back to its horizontal rest position. The lever catch is the small retaining component that holds the lever at the correct horizontal angle against the spring tension - it prevents the lever from drooping below horizontal when the door is not being operated.
Three failure modes require spring cage replacement. Spring fatigue is the most common - after tens of thousands of lever actuations, the torsion spring loses return force and the lever doesn't fully recover to horizontal after each use. Lever catch wear causes the lever to sit at a downward angle at rest rather than horizontal, which creates a visible cosmetic defect and signals the catch is no longer holding properly. Physical damage to the spring cage body itself - from vandalism or over-torque abuse - can misalign the spring and cause erratic lever return behavior.
Schlage ND Series Spring Cage Family: N523-221 and Its Companions
The NDE Series Service Manual (document 015478) documents the complete spring cage catalog for the post-January 2017 ND/NDE platform. The N523-221 is the inside spring cage, but it's one of four spring cage part numbers, each for a different cylinder format and position:
N523-218 = Outside spring cage for all cylinder formats except Yale or Medeco (covers Schlage KIL, FSIC, SFIC, Sargent KIL/FSIC, Corbin Russwin 6-pin FSIC, and all standard outside cylinder positions).
N523-224 = Outside spring cage specifically for Yale 6-pin FSIC, Yale 7-pin FSIC, and Medeco FSIC formats on the outside trim.
N523-221 (this product) = Inside spring cage, less cylinder, universal for all ND functions. Used when the inside trim has no inside cylinder position - which covers all passage, privacy, entrance, storeroom, classroom, and similar functions where the inside lever operates freely without an inside cylinder.
N523-222 = Inside spring cage, with cylinder - for inside trim positions that have an inside cylinder, such as the ND66 double cylinder store function where a key on the inside controls egress.
Schlage ND Series Parts: "Interior Less Cylinder" and Why It Applies to Most Functions
"Interior Less Cylinder" means the inside of the door has no keyed cylinder position in the trim. This covers the vast majority of ND Series functions - ND10 passage, ND30 patio, ND40 privacy, ND44 hospital privacy, ND50/53 entrance, ND80 storeroom, ND70 classroom, and more. All of these have inside levers that are free or push-button operated without a cylinder. They all use the N523-221 spring cage.
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