By Kent · Lock Depot Staff Writer

You don't have to leave the BEST keyway to add a deadbolt

A facility already running BEST interchangeable cores usually solves "we need more security on this door" by asking for another cylindrical lock. But a lot of doors that need a deadbolt already have a working knob or lever on them; a server closet with a cylindrical lock installed years ago, a supply room where the lockset works fine but the door still gets kicked. What that door needs is an auxiliary deadbolt, and the mistake is buying one off a rack that takes a different key than everything else on the property. BEST's 8T-Series tubular deadbolt exists specifically so you don't have to make that trade.

What the 8T actually is

The BEST 8T27KSTK is a standalone tubular deadbolt, single-keyed with an inside turnknob, certified to ANSI A156.36-2010 Auxiliary Locks, Grade 1. It's built to be installed either on its own or alongside a cylindrical lock for extra security on the same door, which is exactly the auxiliary role most of these get bought for. The bolt itself is a 1" throw, 5/8" x 7/8" solid stainless steel bolt, and the housing fits a standard 1" bore on a door built to the usual 1-3/4" thickness. Backset is 2-3/8", and it takes the common STK strike, a 1-1/8" x 2-3/4" rectangular plate that most frames on the property are already prepped for.

None of that is the reason to pick this deadbolt over a generic one from a hardware aisle, though. The reason is the core housing.

The part that matters: it takes your existing BEST core

The 8T27KSTK ships with a 7-pin core housing that accepts all BEST cores, and the core itself is not included, the same way a BEST cylindrical lock ships less-core until you drop your own SFIC in it. That means a deadbolt you're adding to a door already keyed into your BEST system takes the identical core as the lockset, the same key, the same control-key rekey process your locksmith already runs on everything else in the building. You're not introducing a second keyway, a second key ring, or a second call to the locksmith when someone's terminated and the cores need swapping. Pull the core from stock, drop it in the deadbolt, done.

That's the whole case for spending on a branded auxiliary deadbolt instead of whatever's cheapest at the box store: the box-store deadbolt works fine mechanically, but it's a standalone keyway that somebody now has to track separately, forever, on a property that otherwise runs one key system.

Where this one actually gets specified

Interior doors that already have a working cylindrical lock and just need a second layer: IT closets, narcotics cabinets in a clinic, a cash office behind a retail counter. It's not a replacement for the primary lockset and it's not a fire-door part; it's the auxiliary deadbolt you add above or below an existing lock when the door's contents are worth a second bolt. Turnknob operation on the inside means nobody's fumbling for a key to get out, which matters on any door where egress speed is part of the code conversation even if the deadbolt itself isn't the primary means of exit.

Finish-wise we stock it in Satin Chrome (626) and Bright Brass (605), so matching the trim already on the door isn't a special order.

Installing it without opening a second ticket

Because the 8T27KSTK is a standard tubular deadbolt on a 1" bore and a 2-3/8" backset, it drops into the same door prep as any residential-grade deadbolt, no mortise pocket, no special tooling. That's part of why it gets specified as the retrofit answer rather than a mortise deadlock: a maintenance tech can install it in the time it takes to drill and chisel a strike pocket in the jamb, not a half-day mortise job. The push-button housing on the inside doesn't require batteries or wiring either, which matters on interior doors where running power just for a second lock isn't worth the labor.

There's a tradeoff worth naming: a tubular deadbolt is not as resistant to a determined pry attack as a mortise lock body, so it's the right call for an interior door behind a locked suite or a controlled corridor, not the last line of defense on an exterior entrance. Pair it with the door's existing hardware rather than asking it to do a mortise lock's job.

What we stock

The BEST 8T27KSTK deadbolt sits on our BEST hub next to the rest of the line. If the door in question is the primary lockset and not an add-on deadbolt, we've written up the 45H mortise vs 9K cylindrical decision separately, and if you're setting up the core-control side of the system for the first time, the piece on rekeying with an interchangeable core covers how the control key actually works.

One thing worth saying plainly: we don't have a published dimension for anything beyond what's listed here, and we're not going to guess at a spec BEST hasn't put in writing. If your project needs something beyond backset, bolt throw, or strike size, call and we'll confirm it against the manufacturer's cut sheet before you order.

Common questions

Does the 8T27KSTK come with a core?

No. Like BEST's cylindrical and mortise locks, the housing is sold less-core. You supply your own SFIC core, which is the entire point if you're trying to match an existing keying system.

Can this deadbolt replace the primary lock on the door?

It's built and certified as an auxiliary lock, not a primary entrance lockset. Use it alongside an existing cylindrical or mortise lock, not instead of one, if the door needs a code-compliant primary function.

What backset does the 8T27KSTK use?

2-3/8", which is the common backset on most commercial and residential doors. Confirm your door's existing backset before ordering if you're not sure which one you have.

Will any BEST core fit this deadbolt?

The housing is a standard 7-pin SFIC housing built to accept BEST-format cores, the same footprint used across BEST's cylindrical and mortise lines.

What finishes does it come in?

We stock Satin Chrome and Bright Brass. Other finishes may be available to special order; call to confirm before committing a job to one.