By Kent · Lock Depot Staff Writer

The door prep decides this before you do

Walk the building first. Pull a door open, look at the edge, and you have your answer in about four seconds. A mortise pocket routed into the door stile means a mortise body goes back in. A 2-1/8 in cross bore with a 1 in edge bore means cylindrical. That is the whole decision on retrofit work, and no amount of spec sheet reading changes it.

Where it gets interesting is new construction, or a door replacement program where you get to pick the prep. Then you are actually choosing between the BEST 45H7D3H626 mortise lock and the BEST 9K37D14CSTK626 cylindrical lock, and the choice sticks for thirty years.

One note before we go further. Our catalog lists the mortise bodies under a 40H Series heading, so if you search 40H and land on a 45H part number, that is the lock you are looking at. Read the SKU, not the series heading.

BEST 45H vs 9K: where each one belongs

The mortise body carries its latch, its deadbolt, and its trim load inside a steel case buried in the door. The cylindrical body hangs its whole working life off a chassis clamped through two holes. Both are Grade 1. They are not equal.

Put the 45H on exterior doors. Every one of them. Put it on the gym corridor, the cafeteria doors, the main office door that gets pulled two hundred times a day. Anywhere a kid is going to hang off the lever, or a wind gust is going to slam the leaf into the frame, or rain is going to run down the face of the door for eleven years.

Put the 9K on classrooms, offices, storage closets, IT rooms, and interior spaces generally. It is a good lock. It is not a lock I want on a door that takes weather.

Here is the failure I have seen more than any other on school work. A cylindrical lever on an exterior door, west facing, no overhang. Water runs down the door face, finds the cross bore, and sits in the chassis. Three or four winters later the retractor is packed with rust and the latch drags. The lever sags because a hundred pounds of teenager used it as a chin up bar and the chassis spun a quarter turn in the bore, which enlarges the bore, which lets it spin further. Now you cannot fix it with a new lockset. You are fixing the door. I have replaced doors over a lock that cost a fraction of the door, and the maintenance director never forgets that conversation.

So my stance is plain. Do not spec cylindrical on an exterior opening in a school. And do not mix bodies inside one building without a reason you could write on one line of paper. If the ground floor is mortise and the second floor is cylindrical because two contractors bid two different years, your parts cart now carries two sets of spindles, two sets of trim, and two sets of latch fronts. Standardize by function and exposure, not by whoever was cheap that quarter.

The one exception worth making

Rated pairs and doors with narrow stiles sometimes will not take a mortise pocket without eating the structural section of the stile. Check the door manufacturer's prep limits before you commit. That is a real reason to mix. The other guy already installed some is not.

Reading the function code out of the SKU

This is the part that trips people up, and it is worth slowing down on, because getting it wrong means a door that behaves the opposite of what the fire marshal expects.

Take 45H7D3H626 and break it apart. 45H is the mortise series. The 7 is the core prep, meaning it takes a seven pin small format interchangeable core. The D is the function. 3H is the lever and rose design. 626 is satin chrome.

That D is storeroom. Outside lever always locked, key retracts the latch, inside lever always free for egress. Door closes, door is locked, nobody has to remember anything. This is the function you want on most secured openings, because it does not depend on a human doing the right thing at 3pm on a Friday.

Now 45H7AB3H626. Same series, same core prep, same trim, same finish. The function jumped to AB, which is office with deadbolt. An inside thumbturn throws a deadbolt, the outside lever can be locked or left free, and the occupant controls it. That is a principal's office or a records room where somebody wants to lock up and walk away without a key.

The cylindrical side reads the same way. 9K series, then the chassis variant, then 7D for the seven pin core and the storeroom function, then 14C as the lever design and STK as the rose, then 626. Same storeroom behavior as the mortise. Different body, identical logic at the door.

Why the SFIC core is the whole reason to buy either one

Both bodies take the same small format interchangeable core. That is the point. Pull the control key, turn it, the core slides out in your hand, and a new core drops in. No lockset comes off the door. No screws. Nothing hits the floor.

What that means operationally: a teacher loses a key ring on a Tuesday, and you re-key eleven doors before lunch instead of scheduling a two day shutdown. Same story when a custodian leaves. We wrote that workflow up in detail in the SFIC core re-key walkthrough if you want the step by step.

Because the core is common across both bodies, one keyway and one master system covers the whole building regardless of which body is on which door. Your grand master works the mortise on the exterior and the cylindrical on the classroom without a second thought.

Now the gotcha, and it bites people every year. Control keys and operating keys are different animals. If your control key is on the same ring as a teacher's classroom key, you have handed that teacher the ability to pull every core in the building. I have walked into two districts where the control key had been duplicated onto the head custodian's ring for convenience, and in both cases nobody could tell me where the copies went. Control keys live in one place, they get signed out, and they come back. Write it down.

Second gotcha. Order your cores keyed to your existing system, and confirm the keyway before the box ships. A building running one keyway that receives a pallet of cores in a different keyway has bought a very expensive pile of paperweights. Browse the full BEST hardware line and match the keyway you already run.

If you are comparing across brands, the Sargent 10 Line storeroom versus office breakdown covers the same function logic in a different manufacturer's language.

Common questions

Can I use the same core in both the 45H and the 9K?

Yes, as long as both are specified for the seven pin core, which the 7 in the SKU tells you. That shared core is the reason an SFIC lock for a school makes sense in the first place. One keying system, two body styles, one control key.

What does the 7D in the part number actually mean?

The 7 is the core prep and the D is the storeroom function. Storeroom means the outside lever stays locked at all times and the key retracts the latch, while the inside lever always works for free egress.

Why does the catalog say 40H Series on a 45H lock?

That is a listing heading on our side, and the part number is what governs. Order by the full SKU, 45H7D3H626 or 45H7AB3H626, and you get the correct mortise body.

Is the 9K strong enough for a school corridor?

For interior classroom and office doors, yes, it is a Grade 1 lock and it holds up. For exterior doors and heavy abuse corridor openings, go mortise. Weather and lever abuse are what kill a cylindrical chassis.

What does the 14C STK part of the 9K number tell me?

Those are trim tokens, so 14C is the curved lever with return and STK is the rose style. They change how the lock looks and feels at the hand, and they have no effect on function or keying.