Filler plates are flat steel cover plates that attach to a commercial door or frame to conceal unused hardware cutouts. When a door’s lock or latch hardware changes—whether during a retrofit, a hardware upgrade, or a lock conversion—the original cutout in the door edge or frame often remains exposed. A filler plate covers that opening, restoring the door’s structural integrity and finished appearance. Filler plates are required any time a hardware change leaves an open prep in a commercial hollow metal or wood door.
CDF Distributors stocks filler plates for standard mortise and cylindrical lock preps and can include them with any door or frame assembly configured through CDF’s ProBuilder tool at cdfdistributors.com. For help identifying the correct filler plate for your project, call (855) 769-9895 or email sales@cdfdoors.com.
What Is a Filler Plate?
A filler plate is a steel plate designed to cover an unused hardware preparation in a commercial door or frame. When commercial doors are manufactured, the factory cuts specific openings into the door edge and face to accommodate the specified lock or latch hardware. These cutouts are called hardware preps. If the hardware type changes after the door is fabricated—or if an existing door is being retrofitted with different hardware—the original prep may no longer match the new hardware. A filler plate covers the exposed cutout so the door functions and appears as intended.
Filler plates are typically made from the same gauge steel as the door and are finished to match the door surface. They attach with machine screws through pre-drilled holes in the plate and the door edge. Once installed, a filler plate sits flush with the surrounding surface.
When Are Filler Plates Needed?
Filler plates are needed whenever a hardware change leaves an unused cutout exposed on a commercial door or frame. The following table summarizes the most common scenarios that require filler plates.
Scenario | Description |
Lock type conversion | Changing from a mortise lock to a cylindrical lock, or vice versa, leaves the original prep exposed on the door edge |
Hardware upgrade | Replacing an older lock with a different model that does not use the same cutout dimensions |
Door repurposing | Moving a prepped door to a new opening where different hardware is specified |
Frame hardware change | Changing the strike type on a frame, leaving the original strike cutout exposed |
Closer or exit device removal | Removing surface-mounted hardware that leaves behind mounting holes or reinforcement cutouts |
In each of these situations, the filler plate covers the prep that is no longer in use. Leaving a hardware prep uncovered compromises the door’s fire rating (if applicable), security, and appearance.
Types of Filler Plates for Commercial Doors
Filler plates are categorized by the type of hardware prep they are designed to cover. The two most common types correspond to the two standard commercial lock preparations: mortise lock preps and cylindrical lock preps.
Mortise Lock Filler Plates
A mortise lock filler plate covers the rectangular pocket cut into the door edge for a mortise lock body. Mortise lock preps are large rectangular cutouts, typically extending several inches along the door edge. When a door originally prepped for a mortise lock is converted to a cylindrical lock or when the mortise hardware is removed entirely, a mortise filler plate is required to cover the exposed pocket.
Photo or diagram showing a mortise filler plate installed on a door edge, covering the rectangular mortise pocket cutout. This diagram requires CDF approval before inclusion in the production file.
Prep type covered | Mortise lock pocket (rectangular cutout in door edge) |
Typical application | Converting from mortise lock to cylindrical lock, or removing mortise hardware |
Installation location | Door edge |
Attachment method | Machine screws through pre-drilled holes |
Material | Steel, finished to match door surface |
Cylindrical Lock Filler Plates
A cylindrical lock filler plate covers the circular bore hole and latch prep cut into the door edge and face for a cylindrical lever lock or knob lock. Cylindrical preps include a large cross-bore through the door face and a smaller latch bore through the door edge. When a door prepped for a cylindrical lock is converted to a mortise lock or when the cylindrical hardware is removed, a cylindrical filler plate covers the exposed bore holes.
Photo or diagram showing a cylindrical filler plate installed on a door edge, covering the cylindrical latch bore cutout. This diagram requires CDF approval before inclusion in the production file.
Prep type covered | Cylindrical lock bore (circular cutout in door edge and face) |
Typical application | Converting from cylindrical lock to mortise lock, or removing cylindrical hardware |
Installation location | Door edge and/or door face |
Attachment method | Machine screws through pre-drilled holes |
Material | Steel, finished to match door surface |
Mortise vs. Cylindrical Lock Preps: Key Differences
Understanding the difference between mortise and cylindrical lock preps is necessary to select the correct filler plate. The following table compares the two prep types.
Characteristic | Mortise Prep vs. Cylindrical Prep |
Cutout shape | Mortise: rectangular pocket in door edge. Cylindrical: circular bore through door face and edge. |
Lock body location | Mortise: lock body sits inside the door edge. Cylindrical: lock body passes through the door face. |
Door edge appearance | Mortise: large rectangular opening. Cylindrical: small round latch hole. |
Door face appearance | Mortise: no large face bore (trim mounts to surface). Cylindrical: large circular bore on each face. |
Filler plate type | Each prep type requires its own specific filler plate designed to match the cutout geometry. |
How to Match a Filler Plate to an Existing Door Prep
Selecting the correct filler plate requires identifying the existing hardware prep on the door. The following information is needed to match a filler plate to a door.
- Prep type. Determine whether the existing cutout is a mortise prep (rectangular pocket in the door edge) or a cylindrical prep (circular bore through the door face and edge). Visual inspection of the door edge is the fastest way to identify the prep type.
- Door thickness. Commercial doors are typically 1-3/4” thick. The filler plate must match the door thickness to sit flush.
- Door material. Confirm whether the door is hollow metal (steel) or wood. Filler plates are available for both, but the attachment method and plate material may differ.
- Finish. The filler plate finish should match the existing door finish (prime painted, galvanized, stainless steel, or other specified finish).
- Backset. For cylindrical preps, note the backset measurement (the distance from the door edge to the center of the cross-bore). Standard commercial backsets are 2-3/4”.
CDF’s sales team can identify the correct filler plate from a photo of the exposed prep and the door specifications. Contact CDF at (855) 769-9895 or email sales@cdfdoors.com with photos and dimensions for assistance.
Filler Plates and Fire-Rated Door Assemblies
Fire-rated door assemblies require that every component—door, frame, hardware, and accessories—maintains the rated fire resistance of the assembly. An uncovered hardware prep on a fire-rated door is an opening in the door that can compromise the fire rating. Filler plates used on fire-rated assemblies must be listed and labeled for use in fire-rated applications. The following table summarizes fire-rating requirements for filler plates.
Fire Rating Level | Filler Plate Requirement |
20-minute | Filler plate must be listed for use in 20-minute fire-rated assemblies |
45-minute | Filler plate must be listed for use in 45-minute fire-rated assemblies |
60-minute | Filler plate must be listed for use in 60-minute fire-rated assemblies |
90-minute | Filler plate must be listed for use in 90-minute fire-rated assemblies |
3-hour (180-minute) | Filler plate must be listed for use in 3-hour fire-rated assemblies |
Using a non-rated filler plate on a fire-rated door assembly voids the assembly’s fire rating. During fire door inspections (per NFPA 80), inspectors verify that all openings in fire-rated doors are properly covered with listed components. An exposed, uncovered hardware prep is a common inspection failure point.
CDF Distributors supplies fire-rated filler plates that are listed for use in assemblies rated at 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute) levels. Verify all fire-rating requirements with the project specifications and the Authority Having Jurisdiction (AHJ).
Common Lock Conversion Scenarios Requiring Filler Plates
Lock conversions are the most frequent reason filler plates are needed on commercial doors. The following scenarios describe the most common conversions and the filler plates required.
Mortise to Cylindrical Conversion
When a door originally prepped for a mortise lock is converted to accept a cylindrical lever lock, the rectangular mortise pocket in the door edge is no longer used. A mortise filler plate must be installed to cover the exposed pocket before the new cylindrical hardware is installed. The door may also require a new cylindrical bore to be cut through the door face if one does not already exist.
Cylindrical to Mortise Conversion
When a door prepped for a cylindrical lock is converted to accept a mortise lock, the circular bore holes in the door face and the latch bore in the door edge may be partially or fully exposed after the mortise lock is installed. A cylindrical filler plate covers any portions of the original cylindrical prep that remain visible after the new mortise hardware is in place.
Hardware Removal Without Replacement
In some cases, hardware is removed from a door without installing a replacement (for example, removing a lock from a door that will be held open permanently by a magnetic holder). The original prep must still be covered with the appropriate filler plate, especially on fire-rated assemblies where any opening in the door compromises the fire rating.
Ordering Filler Plates from CDF Distributors
CDF Distributors stocks filler plates for standard mortise and cylindrical lock preps in common finishes and door thicknesses. Filler plates can be ordered as standalone items or included with a complete door and frame assembly.
To order, configure your door assembly in CDF’s ProBuilder tool at cdfdistributors.com, where filler plates can be added during the hardware selection step. For standalone filler plate orders or assistance identifying the correct plate for a retrofit, call (855) 769-9895 or email sales@cdfdoors.com.
Frequently Asked Questions
What is a filler plate on a commercial door?
A filler plate is a flat steel plate that covers an unused hardware cutout on a commercial door or frame. When hardware is changed, upgraded, or removed, the original prep (the cutout made for the previous hardware) may be left exposed. A filler plate screws into place over that opening, restoring the door’s finished surface and structural integrity.
When do I need a filler plate?
A filler plate is needed any time a hardware change leaves an unused cutout on a commercial door or frame. The most common scenarios include converting from a mortise lock to a cylindrical lock (or vice versa), upgrading to a different lock model that uses a different prep, repurposing a prepped door for a new opening, or removing hardware without installing a replacement.
What is the difference between a mortise filler plate and a cylindrical filler plate?
A mortise filler plate covers the rectangular pocket cut into the door edge for a mortise lock body. A cylindrical filler plate covers the circular bore holes cut through the door face and edge for a cylindrical lever lock or knob lock. Each type is shaped to match the specific cutout geometry of its corresponding lock prep.
Are filler plates required on fire-rated doors?
Yes. On fire-rated door assemblies, every opening in the door must be covered with a listed, fire-rated component to maintain the assembly’s fire rating. An uncovered hardware prep is an opening that can compromise the rating and will fail a fire door inspection under NFPA 80. Filler plates used on fire-rated doors must be listed for the specific rating level: 20-minute, 45-minute, 60-minute, 90-minute, or 3-hour (180-minute).
How do I identify which filler plate I need?
Look at the exposed cutout on the door edge. A rectangular pocket indicates a mortise prep; a circular bore indicates a cylindrical prep. Note the door thickness (typically 1-3/4” for commercial doors), the door material (hollow metal or wood), and the desired finish. CDF’s sales team can identify the correct filler plate from a photo of the exposed prep.
Can I reuse a filler plate from another door?
A filler plate can be reused if it matches the prep type, door thickness, and finish of the new door. However, on fire-rated assemblies, the filler plate must be listed for the specific fire rating of the assembly. Verify compatibility before reusing a filler plate on a different door.
Do filler plates affect door security?
An uncovered hardware prep weakens the door edge and creates a potential security vulnerability. A properly installed filler plate restores the structural continuity of the door edge. For high-security applications, confirm that the filler plate and its fasteners meet the security requirements specified for the opening.
How are filler plates installed?
Filler plates attach with machine screws through pre-drilled holes in the plate. The plate is positioned over the exposed cutout on the door edge or face, aligned with the existing screw holes or new holes drilled to match, and secured with the provided screws. The installed plate sits flush with the surrounding door surface.
About This Guide
This reference guide is produced by CDF Distributors, a commercial door and frame supplier headquartered in Nashville, Tennessee. CDF fabricates hollow metal door and frame assemblies in-house and supplies hardware, accessories, and components—including filler plates—for commercial door installations nationwide. The information in this guide reflects CDF’s product specifications and industry standards for commercial door hardware.
For questions about filler plates or to order, contact CDF at (855) 769-9895 or sales@cdfdoors.com. Configure complete door assemblies online at cdfdistributors.com using ProBuilder.
