By Kent · Lock Depot Staff Writer

When a housing authority, a dorm, or an older institutional building needs to re-lock a run of doors with mortise locks, the spec often reads Sargent or Schlage out of habit, and the budget flinches. There is a Grade 1 mortise lock that fits the same mortise pocket and does the same job for less: the Arrow BM Series. Arrow Lock is an ASSA ABLOY brand, the same parent as Sargent and Corbin Russwin, and the BM is their heavy commercial mortise line. On a multi-family or institutional door where you need mortise durability but not a premium nameplate, this is the lock I reach for. The only thing you have to get right is the function, and the function lives in the model number.

Why a mortise lock on these doors

A mortise lock installs into a pocket cut into the edge of the door, not the bored cross-hole a cylindrical lock uses. That pocket holds a bigger, stronger lock body with a beefier latch and, in most functions, a deadbolt in the same case. On an apartment entry, a dorm room, or an institutional corridor door, that buys you two things a cylindrical lock does not: the strength and long service life of a heavier mechanism, and a deadbolt-and-latch in one body so the door both latches shut and can be dead-bolted secure. If the building was built with mortise doors, you replace with mortise, because the pocket is already there.

Function: storeroom, apartment, or privacy

Arrow codes the function into the BM number. Read it off how the room is used, and three functions cover most of a building.

BM31, storeroom

The outside lever is always locked and takes a key every time; the inside lever always retracts the latch to exit. There is no unlocked state, so the door defaults to secure and cannot be left accidentally open. The BM31 storeroom function is the answer for a supply room, an electrical or mechanical room, an IT closet, any door that should stay locked to the public.

BM11, apartment / office entry

An entry function with a key outside and a way for the occupant to lock and unlock the door for daily use. It is the workhorse for an apartment entry or an office where the person inside controls the door. The BM11 apartment function is the one most multi-family doors take.

BM27, institutional privacy

A privacy function built for institutional use, locked from inside for privacy with a way for staff to release it from outside in an emergency, and no keyed cylinder in the traditional sense. The BM27 institutional privacy function fits a single-occupant restroom, a patient or resident room, or any door that needs private-but-releasable rather than keyed.

Handing and lever

A mortise lock is handed. The latch bevel and the lock work for a specific swing, so you have to tell us the door's hand: left-hand, right-hand, or the reverse-bevel versions for an outswing door. Get the hand wrong and the latch faces the wrong way. Stand on the outside of the door: if the hinges are on your left it is a left-hand door, on your right it is right-hand. When in doubt, tell us which way it swings and where the hinges are and we work it out.

The lever design rides in the SKU too. HSL is the Hastings lever and VL is the Ventura lever, both clean ADA-compliant commercial levers; pick the one that matches the look you want and keep it consistent across the building so the doors read as one system.

Finish and keying

Finish is the last part of the number. 26D satin chrome is the standard institutional finish, hides wear, and matches most existing hardware; bright brass, satin bronze, oil-rubbed bronze, and stainless are available where the design calls for it. On keying, give us your keyway and master system and we key the locks to the building, or order them to take your existing cores so they fall into your key schedule. On a re-lock the goal is that every new BM keys into the same system you already carry, so tell us up front.

When to step up from the BM

The BM is a Grade 1 mortise lock and it handles institutional traffic. Step past it only when the spec demands a specific premium brand for a warranty or a matching existing system, or when you need an electrified mortise function, an integrated access-control lock, or a specialty function the BM line does not offer. For the ordinary locked storeroom, apartment entry, or institutional privacy door, the BM gives you mortise durability without paying for the nameplate. Match it against a premium line like the Sargent 8200 when the job calls for it, and buy the difference only where the difference earns its keep.

Common questions

What is the difference between storeroom and apartment function?

Storeroom (BM31) keeps the outside lever always locked and needs a key every time, defaulting to secure. Apartment (BM11) is an entry function the occupant can lock and unlock for daily use. Storeroom for supply and utility rooms, apartment for unit and office entries.

Is the Arrow BM a Grade 1 lock?

Yes. The BM is a Grade 1 commercial mortise lock, the top ANSI durability tier, built for institutional and multi-family traffic. It installs into a standard mortise pocket.

Do I have to specify the hand?

Yes. A mortise lock is handed. Tell us the door's hand and swing, or where the hinges sit when you face the door from outside, so the latch bevel and lock work for that opening.

Can Arrow BM locks be keyed to our existing system?

Yes. Give us your keyway and master system and we key them to the building, or order them to accept your existing cores. On a re-lock, tell us up front so every new lock falls into your key schedule.

Lock Depot stocks the Arrow BM Series in storeroom, apartment, institutional privacy, and the other commercial mortise functions, keyed to your system. Start at the Arrow Lock hub, or if you are weighing it against a premium mortise line, read Sargent 8200 Mortise Lock: Which Function for a School Corridor. Or call 877-365-5625 with your door list, handing, and keying, and we will build the locks to match the building.