The Schlage 09-417 is the OEM bulk pack of 10 C603-524 tailpieces for the Schlage D Series key-in-knob cylinder. Each pack contains 10 individual C603-524 tailpieces, which is the correct tailpiece for D Series knob cylinders across all three Schlage modular cylinder families: Classic, Everest 29, and Primus. This is the locksmith-quantity format-10 units per order-for shops and facilities maintaining D Series locks at volume.

The C603-524 is a horizontal-orientation tailpiece specific to the D Series knob. This orientation is confirmed in both the Schlage Everest Full Size Cylinder Service Manual and the Schlage Tailpiece Chart. The orientation matters because the key-in-knob mechanism rotates differently from a key-in-lever mechanism, and the tailpiece geometry must match the lock hub position to transmit rotation correctly. Installing the wrong tailpiece in a D Series knob cylinder will result in a key that turns freely without operating the latch bolt.

Schlage Cylinder Tailpiece: C603-524 vs Other Schlage Tailpieces

The Schlage tailpiece catalog maps one tailpiece to each lock series and cylinder format combination. The C603-524 is the D Knob tailpiece. Here is where the D Series knob tailpiece sits relative to the rest of the Schlage tailpiece family confirmed in the official Schlage Tailpiece Chart:

The A700-031 is for AL Series and A/H Series knobs (except Orbit). The A301-338 is for A/H Series Orbit knobs. The C603-524 (this product, 09-417) is for D Series knobs exclusively. The C604-243 is for D Series levers-a different part number entirely, even though the D Series has both knob and lever variants. The N523-022 is for ND Series levers, which is the vertical orientation tailpiece for the lever-based ND Series.

The most common field error on D Series cylinder service is ordering the C604-243 (D lever) instead of the C603-524 (D knob). If the installed lock uses a D Series knob (round rotating knob, not a lever), this 09-417 pack with C603-524 is the correct part. If the lock has a lever handle in the D Series product family, the C604-243 applies.

Schlage D Series Cylinder: What the Tailpiece Connects

The D Series is Schlage's commercial key-in-knob cylindrical lock line. The cylinder sits inside the knob housing and is retained by the spindle assembly. The tailpiece extends from the rear face of the cylinder plug. When a correct key is inserted and turned, the plug rotates and the tailpiece rotates with it. The tailpiece engages the knob latch cam inside the lock chassis, and that cam retracts the latch bolt.

D Series functions that use the key-in-knob format and require this tailpiece include the D40/D42 entrance function, the D50 storeroom function, the D51PD entrance/office function, the D70 exit function, and the D85 front door function. The D10 passage and D20 privacy functions are non-keyed, so no cylinder or tailpiece applies. All keyed D Series knob functions accept Classic, Everest 29, and Primus modular cylinders-and all require the C603-524 tailpiece.

Schlage Lock Tailpiece: Bulk Pack vs Single Unit

The 09-417 bulk pack format (10x C603-524) is the standard ordering format for commercial locksmiths who carry D Series cylinder inventory. Individual C603-524 tailpieces are included with the Schlage 40-100 multiple tailpiece cylinder assembly, but field service often requires replacement tailpieces as standalone stock. The 10-pack format matches the working inventory needs of shops servicing institutional and commercial buildings with large D Series lock counts.