Author: Site Editor Publish Time: 17-12-2025 Origin: Site
Commercial door hardware can be confusing. You have panic bars, touch bars, crossbars, and a dozen different latching mechanisms. If you are responsible for building security or maintenance, you have likely encountered the term "rim exit device."
Specifically, you might see specifications for a device with a 3/4" throw latch. But what does that mean, and why is it the standard for so many buildings?
A rim exit device is a type of panic hardware mounted on the surface of a door. It secures the opening with a latch bolt that projects into a strike plate mounted on the door frame. The "rim" designation refers to how it is mounted—on the rim or surface of the door—rather than being mortised inside it.
The "3/4" usually refers to the 3/4-inch throw of the latch bolt. This specific length is critical for maintaining fire ratings and security standards, ensuring the door stays latched even if there is slight warping or pressure during a fire event.
This guide breaks down exactly what these devices are, how they compare to other hardware, and how to choose the right trim and features for your facility.
A rim exit device is designed to provide single-point latching for single or double doors. It is the most popular type of panic hardware because it is relatively easy to install and maintain.
When someone presses the push bar (or touch pad) on the inside of the door, the mechanism retracts the latch bolt, allowing the door to swing open freely. This is a life-safety requirement for most commercial buildings, ensuring that occupants can exit quickly during an emergency without needing keys or special knowledge.
Key characteristics include:
Surface Mounting: The entire device sits on the interior face of the door.
Single Point Latching: It latches at one point on the strike jamb (or a mullion for double doors).
3/4" Latch Throw: The bolt extends 3/4 of an inch into the strike, providing robust holding power.
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Choosing between a rim and a mortise exit device is one of the most common decisions facility managers face. While they look similar from the inside (both have push bars), the locking mechanism is completely different.
A rim device bolts to the surface. A mortise device has a lock body that is installed inside a pocket (mortise) cut into the edge of the door.
Here is a quick comparison to help you decide which is right for your application:
Feature | Rim Exit Device | Mortise Exit Device |
|---|---|---|
Installation | Surface-mounted (easier retrofit) | Installed inside door edge (complex prep) |
Latch Bolt | Pullman or Starwheel style (3/4" throw) | Standard latch bolt, often with auxiliary deadlatch |
Door Prep | Minimal drilling required | Requires a specific pocket cutout |
Security | Good (especially with 3/4" throw) | High (intergrated deadbolts available) |
Double Doors | Requires a removable mullion | Can be used with vertical rods or coordinators |
Cost | Generally lower | Generally higher (device + labor) |
Rim devices are ideal for single doors and are often the go-to choice for retrofitting older doors because you don't need to cut a large pocket into the door edge. If you have double doors, you can use two rim devices, but you will need a mullion (a vertical post) in the middle of the opening for the latches to strike against.
You might hear the term "night latch" in conjunction with exit devices. This refers to the function of the exterior trim (the handle or lever on the outside of the door).
A Night Latch (NL) function means the exterior lever or handle is rigid (locked) at all times. The latch bolt can only be retracted by the key on the outside or the push bar on the inside.
This setup is common for doors that are primarily exits but need to be accessible by key for staff. For example, a rear delivery door in a restaurant or an employee entrance in an office building. The term "night latch" implies that the door is securely locked to the public (like at night), but allows key holders to enter.
Unlike a "classroom function" where you can leave the lever unlocked, a night latch ensures the door re-locks the moment you remove the key. This prevents security breaches caused by someone forgetting to re-lock a door.
Yes, absolutely. The "trim" is simply the hardware on the exterior side of the door. While some exit-only doors have no exterior hardware (blank plates), many require access.
Lever trim is popular because it is ADA compliant (easy to grip and turn) and aesthetically pleasing. When selecting lever trim for a rim device, you generally have a few function options:
Passage (14 Function): The lever is always free. Anyone can enter.
Storeroom/Night Latch (03/04 Function): The lever is locked; key retracts latch.
Classroom (08 Function): The key locks or unlocks the lever. When unlocked, the lever works freely without a key.
Because rim devices are often used on exterior doors, the lever trim is susceptible to abuse. Many manufacturers offer "clutching" levers. If someone tries to force the locked lever, it will rotate down without damaging the internal lock mechanism, then snap back into place.
While "3/4" often refers to the latch throw, size also matters regarding door width. Most rim exit devices come in two standard lengths:
3-Foot Device: Fits doors from 30" to 36" wide.
4-Foot Device: Fits doors from 36" to 48" wide.
You can typically cut a device down to fit a smaller door, but you cannot make a short device longer. If you have a 42-inch door, you must order a 4-foot device and cut it down in the field.
For a fire door to effectively stop the spread of fire, it must stay latched even under the immense pressure built up by heat. A 3/4-inch latch throw provides enough engagement with the strike plate to keep the door closed during a fire test. Devices with shorter throws may not pass UL fire codes for certain openings.
Yes, but you need a specific type designed for narrow stile aluminum or glass doors. These devices have a narrower chassis to fit the smaller metal frame surrounding the glass.
No. Vertical rod devices latch at the top and bottom of the door frame. Rim devices latch at the side (the strike jamb). They are two different latching methods. However, on double doors without a mullion, you might see a rim device on one leaf and a vertical rod device on the other (though this is a complex application).
Understanding the mechanics of a rim exit device—from the 3/4" latch throw to the surface-mounted design—helps you make better security decisions. Whether you are replacing a broken unit or outfitting a new building, these devices offer a balance of robust security and life-safety compliance.
If you are unsure which specific model fits your door, start by measuring the door width and checking the fire label on the door edge. When in doubt, consulting a locksmith or hardware specialist can save you from purchasing incompatible trim or devices.
