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Quick Verdict

A US mortise cylinder is a threaded brass body, 1-5/32" diameter at 32 threads per inch, that screws into the lock front and turns a cam at its back. Three choices decide the order: length, cam, keyway. Length runs 1" to 2-1/2" in 1/8" steps: 1-1/8" fits a 1-3/4" door with a standard mortise lock, 1-1/4" to 1-3/8" covers 2" doors and thick trim, 1-1/2" and up is thick doors and deep-set trim. The cam must match the lock, not the cylinder brand: Schlage L escutcheon locks take the L cam (30-004), Schlage rose trims and the L9060 outside take the straight cam (20-001), Sargent ships the 13-0664 offset cam, Adams Rite MS locks take an MS cam. Pins are 6 unless the system says otherwise (Sargent 41 has no 7-pin version; Adams Rite 4036 is 5-pin). A blank hole gets a dummy, not a keyed cylinder.

Mortise vs rim cylinder: how to tell which one your hardware takes

A mortise cylinder is threaded end to end, carries a cam at the back, screws into the lock front or trim, and is held by a set screw in the lock's edge that drops into a groove along the body. A rim cylinder has a smooth body, a flat back with a tailpiece, and two machine screws that pull it against the door from inside through a back plate. Tailpiece and screw holes: rim. Threads and cam: mortise.

Mortise locks, mortise exit device trims, cylinder dogging, and storefront deadlocks and deadlatches (Adams Rite MS and its clones) take mortise cylinders. Rim exit devices with an outside key, rim night latches, and rim deadbolts take rim cylinders; the Von Duprin 98/99 NL function is the everyday case, decoded in the guide to Von Duprin part numbers. Both formats also come as interchangeable-core housings, covered in the post on IC housings for mortise, rim, and key-in-lever: if the building runs SFIC or LFIC cores, buy the matching housing instead.

Mortise cylinder sizes: how to measure and pick the length

Length runs from the face of the head to the back of the threaded body, cam excluded. NLS stocks 1" (Adams Rite), 1-1/8", 1-1/4", 1-3/8", 1-1/2", 1-3/4", and 2-1/2", all on the 1-5/32" x 32 tpi thread (Ilco: 1.150" x 32 UNS), so any length threads into any standard mortise lock; only the reach changes.

The reach has to carry the cam into the lock hub for full bolt travel and land the set-screw groove under the lock's set screw. On a 1-3/4" door with a standard case and sectional rose trim, 1-1/8" does both with the head flush on the rose. From there the rule is additive: each extra 1/8" of door or trim needs 1/8" more cylinder, and a leftover 1/16" is taken up with one blocking ring behind the head, not the next size up. The Schlage 20-001 C 118 is the reference 1-1/8" for L-series rose trims, about $83 at NLS. Corbin Russwin steps the same door through 1000-118, 1000-114, 1000-138, and 1000-112; Sargent through the 41, 42, and 43, then the 52 at 2-1/2", about $122. The exception is the Schlage L escutcheon lock, built around the 1-1/8" 30-004 with the L cam: do not size up for the plate. Too long, and the cam over-travels, the head stands proud, and the set screw lands on thread instead of groove; too short, and the cam never reaches the hub.

Mortise cylinder cams: why the cam is brand-specific and which ones cross

The cam is the plate on the back of the plug that sweeps through the lock's hub when the key turns. Its shape, offset, and orientation belong to whoever designed the lock, so the wrong cam turns freely and moves nothing. The thread is universal; the cam is not.

Schlage splits inside one lock line. The Schlage 30-004 C 118 carries the L cam (L583-254) for L-series escutcheon locks, except the L9060 outside. The 20-001 carries the straight cam (L583-476 at 1-1/8", L583-477 at 1-1/4" and up) for L-series rose trims and the L9060 outside. Put a 20-001 in an escutcheon lock and the key turns without throwing the bolt. Which function and trim you have is decoded in the Schlage commercial lock series guide.

Sargent supplies the 41, 42, 43, and 52 with the standard offset cam 13-0664 when the cylinder is ordered without a lock, so the Sargent 41 1-1/8" 6-pin cylinder is right out of the box for Sargent mortise hardware; it is not offered in 7-pin. Corbin Russwin puts the cam in the part number (the A01 to A04 segment), and the 1000-118 body is listed under all four, so call out the cam with the lock model. Yale's 2153 is listed with the 2160 Yale/Sargent cam, and Falcon's 985 and 986 with the MA cam (see the table).

Cross-brand use means fitting the right cam to a body, not matching brand names. Arrow's MC61 is the explicit case in stock: NLS lists it with five cams on one 1-1/8" 6-pin body, including 006 for Schlage locks and AR18 for Adams Rite locks. Beyond those stated cross-fits, treat every cam as lock-specific and confirm it against the template or with the NLS desk.

Adams Rite MS deadlocks and deadlatches take an MS cam, and the Adams Rite 4036-01-02 is the factory 1" x 1-5/32" cylinder for them: 5-pin, aluminum shell in 628 clear, 313 dark bronze, or 335 black anodized, 1/4" trim ring for a 1-3/4" door, cam selected to suit the lock. This SKU is keyed alike in pairs for double-cylinder deadlocks, about $38 at NLS.

Stocked mortise cylinders by brand, length, cam, and keyway

Read "Ships as" before ordering ten. KD with 2 keys works on arrival; 0-bitted (Corbin Russwin 1000, options on Sargent 41 LA and Yale 2153) means zero-depth pins and blank keys, pinned to your system by a locksmith first, and 1-bitted (Sargent) is the same at one depth. The keyway has to match the blank family already in the building; the codes above are mapped to systems and blanks in the guide to commercial cylinder keyways and keying compatibility. Finish suffixes are BHMA codes (626 satin chrome, 613 oil-rubbed bronze, 630 satin stainless, Sargent 32D).

Dummy mortise cylinders: when a blank hole needs a plug, not a lock

A dummy is a threaded body with a solid face: no plug, keyway, pins, or cam. It fills a cylinder hole the function does not use: the outside of a trim ordered with a hole for a function with no outside key, the second hole on an exit device trim, a cylinder-dogging prep you do not want to key. Privacy and indicator functions are the common case; the function chart in the occupancy indicator locks guide shows which ones end up with a blank hole.

Buy it in the same length as the keyed cylinder opposite. The Kaba Ilco 7200DC 1-1/4" dummy is the stock answer, solid brass on the 1.150" x 32 UNS thread with a 1.360" face, about $10 at NLS; the 7280DC is the same part at 1-3/4", both in 26D, 03, 04, 10, 10B, and 26. For BEST-pattern openings, the BEST 1E04-RP2 is a 1-1/8" brass or bronze dummy with the RP2 ring package. A dummy adds no security: never use one to paper over a missing key function.

Rim cylinders and rim housings for rim exit devices

A rim cylinder mounts through the door: the tailpiece passes through the device's outside case or trim to the latch mechanism, and two machine screws from inside pull it tight against a back plate. Fit comes down to tailpiece orientation (horizontal or vertical, set by the device) and screw pattern. The Sargent 34 LA rim cylinder is the template: solid brass, 6-pin, horizontal tailpiece only, 27/32" screw pattern for through-bolted Sargent exit devices, furnished with No. 97 rosette, compression spring, break-off screws, and back plate. Corbin Russwin's 3000-200 ships 0-bitted in 6-pin (3000-200-6) and 7-pin (3000-200-7) for exit devices and trim.

For interchangeable cores, buy a rim housing. Schlage's 20-057 is an FSIC rim housing with core and a convertible tailpiece for exit devices and aluminum doors; its 80-116 is the SFIC version with a horizontal tailpiece and a disposable construction core. The Sargent 70-34 SFIC housing takes 6- or 7-pin cores, ships with a plastic construction core, and has mounting holes located to match Sargent hardware. The Falcon C953 SFIC housing is sold less core for 6 or 7 pins, with a horizontal tailpiece changeable to vertical in the field. Which core format you have is settled in the post on SFIC vs LFIC interchangeable cores. A rim cylinder that turns but does not retract the latch almost always has the tailpiece in the wrong orientation or too short.

Common mistakes

1. Sizing by door thickness alone. Trim thickness and hub depth add to the reach: thick cast trim on a 1-3/4" door can need 1-1/4".

2. Assuming the cam follows the brand. Schlage alone splits between the straight cam (20-001) and the L cam (30-004); Corbin Russwin's A01 to A04 code has to be on the order.

3. Stacking blocking rings. One ring corrects 1/16" to 1/8"; two or three move the set-screw groove out of reach.

4. Ignoring the set screw. If the groove is not under it, the cylinder can be unscrewed from outside with a pipe wrench.

5. Ordering 7-pin where the body does not exist (Sargent 41 is 6-pin only), or expecting 0-bitted Corbin Russwin cylinders to work before pinning.

6. Wrong tailpiece orientation on a rim cylinder. The Sargent 34 is horizontal only; devices that want vertical get a convertible housing (Schlage 20-057, Falcon C953).

FAQ

What size mortise cylinder fits a 1-3/4" door? 1-1/8" for a standard mortise lock with rose trim (Schlage 20-001 C 118, Sargent 41, Corbin Russwin 1000-118); 1-1/4" for thick cast or exit device trim; 1" with a 1/4" ring for an Adams Rite MS storefront lock.

Are mortise cylinder threads the same across brands? Yes for standard US commercial cylinders: 1-5/32" diameter at 32 threads per inch. Any body threads into any standard mortise lock; length and cam are what change.

Can I put a Schlage cylinder in a Sargent lock, or the reverse? Only with the right cam; the body threads in, the cam decides whether it operates the lock. NLS lists explicit cross-fit cams on the Arrow MC61 (006 for Schlage, AR18 for Adams Rite); confirm any other pairing against the template.

What is a dummy mortise cylinder for? Filling a hole the function does not use: a keyless outside on a privacy or indicator function, the second hole on a trim, an unkeyed dogging prep. Match the keyed side's length (Ilco 7200DC 1-1/4", 7280DC 1-3/4"). It provides no security.

Rim or mortise cylinder for a panic bar? Rim devices with an outside key (Von Duprin 98/99 NL, through-bolted Sargent devices) take rim; mortise exit devices, mortise trims, and cylinder dogging take mortise. Two screw holes and a tailpiece slot mean rim; a threaded hole with a set screw means mortise.

Next step

Pull four things before ordering: lock model and trim style, door thickness, the keyway on the existing keys, and whether each hole is keyed or blank. Then filter the mortise cylinders category at NLS by brand and length, add a dummy for any blank side, and pick the keying on the listing (KD, KA, or 0-bitted for your locksmith to pin). If the cam code is the open question, call the commercial desk at 718-814-6300 with the lock model in hand. Orders placed before 3:00 p.m. EST ship the same day by UPS or FedEx from Brooklyn, ground shipping is free at $450 and up, and stock items return within 30 days uninstalled (25% restocking on lock parts). National Lock Supply is family-owned across three generations, carries 40+ brands, and sells online to pros without a dealer account.