BEST 1EA6A4 Mortise Cylinder - Thumb Turn

The BEST 1EA6A4 is the thumbturn version of BEST's 1E Series mortise cylinder - machined brass body, 6-pin SFIC interchangeable core housing, A keyway, 1-1/8-inch length, 1-5/32-inch diameter, with a diagonal set screw and multiple cam options. If you searched "mortise cylinder thumbturn", "mortise thumbturn lock", "mortise thumbturn cylinder", "best lock cylinders", or "best cylinder" - this is the product.

What a Mortise Thumbturn Cylinder Is

Every other product page for this cylinder lists it without explaining what a thumbturn mortise cylinder actually does. Here is that explanation.

A standard mortise cylinder - the keyed version - has a keyway on the face. You insert a key, the plug rotates, the cam at the back turns, and that cam drives the locking mechanism. The whole purpose is key-controlled rotation.

A mortise thumbturn cylinder replaces the keyway and plug with a thumbturn lever or knob on the face. You twist the thumbturn by hand - no key - and the same cam at the back turns to drive the same locking mechanism. There is no keyway because no key is needed on this side.

The most common application is the inside face of a mortise lock door. The outside face of the door gets a keyed cylinder (1E64) for key entry. The inside face gets the thumbturn cylinder (1EA6A4) so the occupant can lock or unlock the deadbolt manually from inside without a key. On a residential-style front door spec, a commercial restroom, an apartment entry, or any door where inside occupant control of a deadbolt or latch is required, the thumbturn cylinder fills the inside cylinder position while the keyed cylinder fills the outside.

"Best Cylinder" and "Best Lock Cylinders": The 1E Series

The BEST 1E Series is BEST's primary mortise cylinder line for standard commercial applications. It's been the institutional standard across universities, hospitals, government buildings, and commercial campuses for decades. When architects and locksmiths specify BEST mortise cylinders, 1E is the series they're ordering unless a specialized variant is required.

All 1E cylinders - keyed and thumbturn - share the same 1-5/32-inch diameter body, making them interchangeable in any mortise lock housing that accepts standard commercial mortise cylinders. They drop into BEST mortise lock cases, Arrow BM Series cases, Sargent, Corbin Russwin, Yale, and most other major mortise lock housings as long as the correct cam is specified.

1EA6A4 Model Decoded

1E - BEST 1E Series mortise cylinder. Standard for all commercial mortise applications.

A - A keyway designation in the housing. Even though this cylinder doesn't have a functioning keyway (it's a thumbturn), the housing retains the A keyway format designation for catalog ordering purposes.

6 - 6-pin format.

A4 - The thumbturn designation within the 1E Series. A4 identifies this as the thumbturn variant.

Cam and finish designations follow with a dash - for example, 1EA6A4-C140RP2-626 specifies the C140 cam with RP2 trim in satin chrome finish 626.

Cam Selection: The Ordering Decision That Matters Most

Every cam listed for the 1EA6A4 drives a different locking mechanism - ordering the wrong cam means the cylinder won't operate the lock correctly. Here are the most commonly specified options:

C140 - Standard cam for most BEST mortise lock applications. Correct for the majority of BEST 1C, 6E, 7E, and 9E series mortise locks. The C140 is the default specification when the lock type is a standard BEST mortise.

C4 - The "standard 1E-C4 cam" referenced in BEST's catalog for standard mortise applications. Used with BEST's own 1E-series mortise lock housings in their most common configuration.

C428 - For specific BEST mortise lock functions that require a different cam profile and rotation arc.

C413 - For additional specific mortise functions where the latch or deadbolt requires a distinct cam geometry.

C181 / ADA thumbturn - The ADA-compliant thumbturn variant with a larger, lever-style thumbturn (versus the standard round knob) that meets ADA gripping requirements for accessible doors.

For Adams Rite mortise locks, a dedicated Adams Rite-compatible cam is required - BEST cylinders can be altered to function with Adams Rite hardware, but the cam must be specified to match the specific Adams Rite model in use.

Do not attempt to use one manufacturer's cam on another manufacturer's cylinder. The cam attachment geometry and the drive pin specifications are manufacturer-specific.

Diagonal Set Screw: Why It's a Security Feature

Most mortise cylinders use a set screw to lock the cylinder in the housing so it can't rotate once installed. The BEST 1E Series mounts this set screw diagonally - at an angle through the cylinder wall rather than straight through.

The diagonal mounting serves two purposes. First, it creates a more positive mechanical lock against the housing because the angled screw bears against the housing groove differently than a radially-mounted screw - it resists both rotation and pullout under attack. Second, it makes it harder to access and remove with standard straight-drive tools because the approach angle is off-axis. On a cylinder being attacked by someone trying to spin it or pull it out, the diagonal set screw adds meaningful resistance.

SFIC Core Integration: Key Into Any BEST System

The 1EA6A4 features the BEST interchangeable core housing - the same SFIC format as the 1E64 keyed version. This matters for the thumbturn position for one specific reason: even though the thumbturn side doesn't use a key for daily operation, the SFIC housing means the core slot is still accessible for a control key. On certain BEST mortise lock configurations, the inside cylinder position can be combinated for keyed access as well - the core housing gives the facility manager the option to add key control to the inside position later if the application changes.

The cylinder can be masterkeyed into any existing BEST key system, and the SFIC housing accepts both 6-pin and 7-pin BEST cores.

Finishes and Lengths

Standard length: 1-1/8 inch (most common, fits standard 1-3/4" doors).

Other available lengths: 1-1/4 inch and extended lengths for thicker doors.

Finishes: 606 (satin brass), 612 (satin bronze), 613 (dark bronze oil rubbed), 622 (antique nickel), 625 (bright chrome), 626 (satin chrome), and others. Specify the finish suffix when ordering (e.g., -626 for satin chrome).

Specifications

Model: BEST 1EA6A4

Series: BEST 1E Mortise Cylinder - thumbturn

Format: Thumbturn (inside operator, no key required)

Pins: 6-pin SFIC housing

Length: 1-1/8" standard

Diameter: 1-5/32" (29.37mm)

Material: Machined brass or bronze bar stock

Security: Diagonal set screw - holds cylinder in housing under rotation and pullout attack

Core: BEST SFIC interchangeable core - masterkeyed into any BEST system

Cam Options: C140, C4, C428, C413, C181 (ADA), others - specify for lock type

Keyed Equivalent: 1EA64 (keyed) / 1E64 (keyed, standard mortise)

Finishes: 606, 612, 613, 622, 625, 626 - specify as suffix

Compatible Locks: BEST mortise locks, Arrow BM Series, Sargent, Corbin Russwin, Adams Rite (with correct cam), and other mortise housings accepting standard 1-5/32" cylinders

American Locksets has stocked BEST Access Systems cylinders since 2001.