Arrow BM Series Front Door Mortise Lock, X Lever, L Rose, Satin Chrome

That's exactly what the BM Series is built for. Standard door thickness is 1-3/4 inches and the backset is 2-3/4 inches, which is the normal commercial mortise prep. Other door thicknesses are available through the factory as a special order, but the catalog build is 1-3/4. The armored front measures 8 x 1-1/4 x 3/32 inches and works on flat doors as well as doors beveled 1/8 inch in 2 inches, so a standard beveled commercial door needs no extra work.

It ships handed, but it is field reversible and you can re-hand it without opening the lock case. That matters on a retrofit where you measure the opening wrong, or on a job where you are hanging a mix of left and right hand doors off one carton. No disassembly, no returns.

BM21 is the classroom function. The key in the outside cylinder locks and unlocks the outside lever; the inside lever always retracts the latch for free egress. Nobody can lock the door from inside the room, which is why it is the standard for corridor-side classroom doors in schools. If you need to lock the door from inside without opening it, classroom function is the wrong choice and you want a different BM function number.

The latchbolt is stainless steel, two piece mechanical with an anti-friction insert, measuring 5/8 x 1 inch with a 3/4 inch throw. The deadbolt is one-piece stainless, 19/32 x 1-1/4 inch with a full 1 inch throw. An existing ANSI mortise strike prep will take it: the supplied strike is wrought brass or bronze, ANSI straight lip, 4-7/8 x 1-1/4 inches with 1-1/8 inch lip to center. If your frame has a deeper reveal, longer lip lengths and an ANSI wrought strike box are available as options.

Yes, and the keying options are broad: master keying, construction master keying, visual key control, concealed key control, and high security cylinders. If your facility runs small format interchangeable core, the BM Series takes Arrow Pointe and Pointe Flex IC. Two nickel silver keys come standard with the lock.

The BM Series lock case is 5-7/8 x 4 x 15/16 inches, heavy gauge steel with a zinc dichromate finish for corrosion resistance. If you are cutting a new pocket or checking an existing one, that 15/16 inch case thickness is what has to clear inside the door edge. The armored front that covers the mortise is 8 x 1-1/4 x 3/32 inches.

There is an auxiliary latchbolt with a 9/16 inch effective throw that provides 3/8 inch of effective auxiliary latch deadlocking. When the door is closed and the auxiliary bolt is depressed by the strike, the main latch cannot be pushed back. That is the anti-shim feature on an exterior or corridor opening, and it is why the auxiliary bolt has to land on the strike face, not in the strike cutout.

Center to center from hub to cylinder is 3-5/8 inches, and hub to turnpiece is 2-7/16 inches. Those are the numbers you need when you are drilling a door for escutcheon or rose trim, or checking whether existing through-bores line up. The lever hub itself is nickel steel, 5/16 inch.

Mortise is the heavier answer. The BM Series is built for heavy duty use in schools, hospitals and commercial buildings where security, durability and low maintenance matter, and it gives you a latchbolt and a separate 1 inch throw deadbolt in one case. A cylindrical lock only needs two cross bores and goes in faster, but it has no deadbolt and less material behind it. The tradeoff is the door prep: mortise needs a pocket 5-7/8 x 4 x 15/16 inches routed into the edge, so on an existing cylindrical-prepped door you are either buying a new door or filling and re-prepping.

It is the X lever on an L rose in 26D satin chrome, the standard commercial finish that matches most existing door hardware, hinges and closers in a school or office building. The faceplate is wrought brass or bronze, machine screwed to the front of the lock case, and the strike is the same material. If you are standardizing a building, 26D is the finish to spec across the openings.

This is commercial grade hardware, catalogued for commercial use and built for the traffic in schools, hospitals and commercial buildings. It will function on a residential door, but you need a 1-3/4 inch thick door with a mortise pocket, which most houses do not have, and the lever trim and 2-3/4 inch backset are commercial dimensions. For a high-traffic multi-family or apartment entry it makes sense; for a typical single-family interior door it is the wrong part.