SecurityParts.com carries parts for three commercial cylindrical lock series: the Schlage ND Series Grade 1 (24 mechanical functions, beyond-Grade-1 strength), the Schlage ALX Series Grade 2 (single modular chassis, field function change), and the Falcon T Series Grade 1 (extra heavy-duty, accepts any manufacturer's cylinder). The function code determines the correct chassis, spring cage, and trim components. Never order parts by appearance alone. The ND Series and ALX Series share lever styles for visual suiting but use different chassis and function kits. Parts that fail first are the spring cage, latch, and cylinder. Always confirm function code and manufacture date before ordering.

Commercial cylindrical locks are on more doors per building than any other lock category. Office corridors, storage rooms, restrooms, classrooms, patient rooms, server closets. Every one of those doors has a chassis, a latch, a spring cage, a cylinder, levers, and a strike. When one component wears or fails, replacing it correctly the first time depends entirely on having the right series and function code before you open any catalog page.

SecurityParts.com stocks parts for the three most widely installed commercial cylindrical lock series: the Schlage ND Series, the Schlage ALX Series, and the Falcon T Series. This guide covers every component, the function codes that determine which parts you need, what fails first, and how to order without a return. Browse the complete cylindrical lock parts catalog at SecurityParts.com for interactive diagrams on every model.

The Three Series at Security Parts: How They Compare

Schlage ND Series: Understanding Function Codes Before Ordering Parts

The ND Series function code is the most critical piece of information needed before any parts order. The function code determines the chassis configuration, the spring cage type, and which trim components are compatible. Ordering a spring cage or adjustment plate from the wrong function creates a non-functional lock even when the physical parts fit together.

The Most Common ND Series Functions in Commercial Buildings

Vandlgard: What It Is and Why It Matters for Parts Ordering

Vandlgard is a Schlage-patented feature that prevents forced lever torque from retracting the latch. On a standard ND Series lock, applying enough sustained downward force to the outside lever can, in some cases, retract the latch through the mechanical connection between the lever and the chassis. Vandlgard adds a clutch mechanism that breaks the lever-to-chassis connection before that force threshold is reached, while the lever can still operate normally when the door is unlocked.

Vandlgard function suffixes are ND91 (entrance/office), ND92 (entrance), ND94 (classroom), ND96 (storeroom), and ND97 (corridor). The Vandlgard function is field-selectable on the ALX Series, which means you can enable or disable it without ordering a different lock. On the ND Series, the Vandlgard feature is built into the function-specific chassis and cannot be retrofitted to a standard chassis without replacing the chassis assembly.

Most current institutional specifications for K-12, higher education, and healthcare require Vandlgard on classroom, storeroom, and secured office functions. If your building was originally specified with Vandlgard functions, all replacement parts must be sourced for the Vandlgard version of that function, not the standard version.

Every Replaceable Component in Commercial Cylindrical Locks

Chassis Assembly

The chassis is the internal mechanism housing that sits inside the door bore and contains the locking mechanism, the spindle engagement, and the spring return components. The chassis determines the function of the lock. It is not universal across functions on the ND Series. An ND50 chassis is configured differently from an ND70 or ND80 chassis, even though they look similar from the outside.

The Schlage ND Series chassis is zinc and steel with zinc dichromate plating for corrosion resistance. Door thickness accommodation is 1-3/4 inch standard with spacer kits available for 1-3/8 inch through 1-11/16 inch doors. The ALX Series uses a single chassis design that accommodates most functions, which is its key advantage for inventory management: one chassis type covers most of a building's lock schedule.

Replace the chassis when the internal mechanism fails to hold the locked state, when the spindle has developed severe play that cannot be addressed by spring cage replacement, or when a function conversion is required on the ALX Series. On the ND Series, function changes require a complete chassis replacement along with matching trim.

Spring Cage Assembly

The spring cage holds the lever in the horizontal position and provides the return force that brings the lever back after it is depressed. This is the most frequently replaced component on high-use cylindrical locks. Spring cage failure presents as lever sag, lever that does not return fully after being depressed, or a lever that rattles in the horizontal position.

Both Schlage ND and ALX Series use Grade 1 compression springs in the spring cage assembly specifically to resist lever droop under sustained use. The Falcon T Series uses a compression spring behind the cylinder that serves a similar function. When replacing a spring cage, confirm whether the outside or inside spring cage is failing before ordering. Both sides have their own spring cage assembly and they are not interchangeable with each other.

Latch Assembly

The latch is the spring-loaded bolt that extends from the door edge and clicks into the strike plate on the frame. On commercial cylindrical locks, the standard latch is a deadlatch, not a simple spring latch. A deadlatch has a plunger alongside the latch bolt that, when depressed by the strike plate on closing, prevents the latch bolt from being pushed back by a credit card or similar tool from the latch side of the door.

The Schlage ND Series default latch is part 13-247 with a 2-3/4 inch backset and 1-1/8 inch by 1-1/4 inch faceplate. The Falcon T Series default latch is part 23981145, a deadlatch with 2-3/4 inch backset and 1-1/8 inch by 2-1/4 inch square corner faceplate. Always confirm the backset (2-3/4 inch standard, 2-3/8 inch available) before ordering a latch replacement.

Latch failures on commercial cylindrical locks include the latch not retracting smoothly when the lever is depressed, the latch bolt not springing back after depression, and the deadlatch plunger binding or not depressing correctly. A latch that does not retract when the lever operates normally indicates the latch has failed, not the chassis. A latch that retracts but the lever feels stiff typically indicates the spring cage, not the latch.

Strike Plate

The standard ND Series strike is part 10-025, an ANSI curved lip strike, 1-1/4 inch by 4-7/8 inch, no box. The Falcon T Series default strike is part 5164, ANSI 1-1/4 inch by 4-7/8 inch with 1-3/16 inch lip length. The ALX Series uses the same ANSI curved lip strike as the ND Series.

Strike replacement is required when the strike is damaged by door misalignment, when the latch bolt fails to engage cleanly due to strike wear, or when a door handing change requires a different strike orientation. An ANSI box strike is used when hollow metal frame reinforcement is required. Always measure the existing frame cutout before ordering a strike replacement to confirm whether a standard or box strike fits the existing frame preparation.

Cylinders and Cylinder Formats

All three series at SecurityParts.com support multiple cylinder formats. Understanding the cylinder format installed is essential before ordering any cylinder replacement.

The Falcon T Series is specifically designed to accept cylinders from competing manufacturers including Sargent and Corbin Russwin in addition to Schlage. Some cylinders require modification of the lock for proper fit. Always specify the cylinder manufacturer when ordering a T Series with a non-standard cylinder.

Levers, Roses, and Trim

Levers on the ND Series are available in 9 designs including Athens, Rhodes, Sparta, Saturn, Broadway, Latitude, and Omega styles. The ALX Series shares these same lever designs, which is the visual suiting feature that allows mixed Grade 1/Grade 2 buildings to maintain a consistent appearance. Levers are pressure cast zinc finished to match mating parts.

The rose is the circular cover plate that conceals the chassis bore and the mounting screws on each side of the door. The ND Series rose is 3-7/16 inch standard diameter. The ALX Series rose is 3-7/16 inch standard, matching the ND Series for a seamless appearance when both are installed in the same building.

On the ALX Series, an optional break-away feature is available on Rhodes levers for most locking functions. When excessive torque is applied, the handheld portion of the lever breaks away from the shank, protecting the internal chassis from the torque damage that would otherwise require chassis replacement. This is a documented X Factor feature of the ALX Series and worth specifying on doors that receive frequent abuse.

Schlage ALX Series: The Modular Advantage and What It Means for Parts

The ALX Series modular design is the most significant feature for facilities managers and locksmiths who maintain large building inventories. A single chassis type supports most functions and all cylinder applications. This means a building can stock one chassis type and change functions in the field when a room's use changes, rather than ordering a new configured lock for every function change.

How In-Field Function Change Works

The ALX Series function is determined by a separate function kit that drops into the chassis. Changing from an ALX50 office function to an ALX70 classroom function requires the ALX70 function kit, not a new lock. The chassis stays. The lever stays. Only the function kit changes. This approach reduces inventory carrying costs, eliminates lead time waiting for factory-configured stock, and lets locksmiths carry a small number of kits on their truck rather than multiple configured lock units.

The installation sequence is designed for this: drop in the interior lever, install the function into the chassis, place the chassis in the door bore with the outside lever on the spindle, drop in the latch, drop in the cylinder or exterior function part. The separate compartment packaging keeps parts organized and prevents the small-part loss that often delays field service calls.

Captured Screws

The ALX Series uses captured screws in the latch, strike, and inside spring cage. Captured screws are retained in the component and do not fall out when the component is removed from the door. This eliminates the most common cause of rework on cylindrical lock service calls: small screws falling into wall cavities or onto floors during disassembly. On a building with dozens or hundreds of locks being serviced in a single shift, this feature has a real cumulative impact on service time.

Falcon T Series: The Multi-Cylinder Advantage and Pressure Release

The Falcon T Series occupies a distinct position in the cylindrical lock market. It is Grade 1 extra heavy-duty, designed for the highest-abuse institutional applications including government and military facilities, correctional housing, and any environment where locks receive deliberate physical attack rather than normal use.

Pressure Release Lever Rotation

The Falcon T Series includes Pressure Release lever rotation as a standard feature. When excessive torque is applied to the outside lever beyond the normal operating range, the lever rotates to a stop position that breaks the mechanical connection to the chassis rather than transmitting that force into the internal mechanism. This prevents the internal chassis damage that requires replacement after a forced entry attempt. The Pressure Release mechanism returns to normal operation after the excessive force is removed, without requiring any parts replacement, which is what makes it a standard feature rather than a consumable component.

Universal Cylinder Acceptance

The Falcon T Series is designed and marketed specifically on its ability to accept cylinders from competing manufacturers. In retrofit applications, this means a facility with an existing Corbin Russwin or Sargent key system can install T Series locks and retain their existing key system without rekeying. The T Series ships with 6-pin chambers drilled in 5-pin configuration as standard. 6-pin pinning is available at no extra cost when specified at ordering. This cylinder flexibility is the primary reason the T Series is specified on government and military retrofit projects where key system continuity is a security requirement.

Parts That Fail First: Realistic Replacement Frequency

Here is the actual field replacement order across all three series based on service call frequency.

1. Spring cage assembly. The most common replacement item on cylindrical locks with more than five years of high-traffic use. Lever sag, incomplete lever return, and lever rattle all trace to spring cage fatigue. Always try spring cage replacement before ordering a chassis.

2. Latch assembly. Latch bolts wear at the tip from repeated contact with strike plates that are slightly misaligned. The deadlatch plunger binding is a specific failure mode on latches that have been in service for more than 10 years without lubrication. Latches are inexpensive individual components and should be replaced rather than lubricated repeatedly once wear is visible on the bolt tip.

3. Cylinder. Cylinders wear from key insertion, especially in high-traffic entry doors. Signs of cylinder wear include a key that operates stiffly, a key that only works in one rotational direction, or a cylinder that spins without retracting the latch. FSIC and SFIC cylinders in interchangeable core systems can be replaced in seconds without disassembling the lock. Conventional cylinders require pulling the lock for cylinder removal.

4. Lever assembly. Levers bend, crack, or have their finish worn off from high-contact use. Lever replacement is cosmetic when the lock function is not impaired. Lever replacement is functional when a bent lever fails to return to horizontal or fails to fully depress the chassis mechanism on operation.

5. Strike plate. Strike wear accelerates when the door has settled and the latch bolt contacts the strike lip rather than entering the pocket cleanly. A worn or deformed strike allows a door that feels locked to actually be holdable open with sustained pressure. Strike replacement is inexpensive and should be done proactively when door alignment has been corrected.

How to Identify Your Lock Model Before Ordering

The model label is on the chassis body, visible when the inside lever and rose are removed. The label shows the series designation (ND Series, ALX Series, T Series), the function code (ND70, ALX50, T581), the finish code (626, 622, 619), and the handing if the lock is handed. For Schlage ND Series, the manufacture date is also on this label and is critical for selecting the correct parts revision.

If the label is worn or missing on an older ND Series unit, the function can often be determined by testing: the way the inside and outside levers behave without a key present tells you the function. A lever that is always free on one side and always locked on the other is storeroom (ND80). A lever that locks with a button from inside is entrance/office (ND50). A lever that locks from the outside with a key but the inside is always free is classroom (ND70).

For Falcon T Series locks, the model is stamped or cast into the chassis body itself. Common T Series model codes include T501 (passage), T521 (privacy), T561 (storeroom), T571 (classroom), and T581 (entrance/office).

SecurityParts.com organizes all three series in the cylindrical locks parts catalog by brand and model with interactive exploded diagrams. For Schlage commercial hardware parts including the ND Series, ALX Series, and Schlage B Series deadbolts, browse the Schlage catalog. For Falcon commercial hardware parts including the T Series and Falcon exit devices, browse the Falcon catalog. Pre-order support is available at 845-935-0301 or through the contact page.

Related Parts and Products at SecurityParts.com

Cylindrical locks are part of a complete commercial door opening. The complete assembly on most institutional doors also includes a door closer, exit device, or mortise lock at higher-security openings.

For Schlage L Series and Falcon MA Series mortise lock parts on high-security and main entry doors in the same facility, browse the mortise locks catalog. For Schlage B Series deadbolt parts on doors that use a deadbolt alongside a cylindrical lock, browse the deadbolts catalog. For LCN door closer parts on any door with automatic closing hardware, browse the door closers catalog. For Von Duprin and Falcon exit device parts on egress doors in the same building, browse the commercial exit devices catalog. For Von Duprin electric strike parts on access-controlled entries, browse the electric strikes catalog.

Browse the complete all products and parts catalog to source Schlage, Falcon, Von Duprin, LCN, and Detex in a single session.