Why Frame Strike Preparation Is a Decision, Not a Default
This article is for commercial contractors, door frame suppliers, and facility managers who need to understand how strike preparations are specified and ordered on hollow metal frames -- and what goes wrong when the frame prep and the hardware do not match. Getting strike prep right before the frame ships is far cheaper than cutting steel on the jobsite or waiting on a replacement jamb.
What Is a Frame Strike Preparation?
A frame strike preparation -- sometimes called a frame strike prep or strike cutout -- is the factory-machined opening, reinforcement box, and tapped screw holes built into the lock jamb of a hollow metal frame to receive the strike plate for a lockset, deadlock, exit device, or electric strike. The prep is sized, located, and reinforced during frame fabrication to match the hardware specified on the door schedule.
Because hollow metal frames are typically ordered and fabricated weeks before hardware is selected or delivered, a mismatch between the frame prep and the actual strike causes real problems: field cuts that compromise the frame reinforcement, incorrect centerline heights that place the bolt outside the strike opening, or strike backsets that leave the bolt hitting the frame face instead of engaging cleanly.
The ANSI Strike Designation System: What E1, E2, E3, and E4 Mean
Frame manufacturers use ANSI A115 designations to identify standard strike preps. Understanding these codes is essential when reviewing a door schedule or submitting a frame order.
E1 -- Standard Latch Strike (ANSI A115)
- Dimensions: 1-1/4 in. wide x 4-7/8 in. tall reinforcement cover box
- Cover box depth: 1-1/16 in., fabricated from 16-gauge steel
- Screw holes extruded to provide thread depth equivalent to 12-gauge plate
- Standard strike backset: 5/16 in. on a 1-3/4 in. door
- Standard centerline height: 40 in. from bottom of frame on a 1-3/4 in. door
- This is the most common commercial strike prep -- used with cylindrical and mortise locksets on the vast majority of interior and exterior commercial doors
E2 -- Smaller Latch Strike
- Dimensions: 1-1/8 in. wide x 2-3/4 in. tall cover box, 1 in. deep
- Standard backset: 3/8 in. for 1-3/4 in. doors; 3/16 in. for 1-3/8 in. doors
- Standard CL: 40 in. from bottom on 1-3/4 in. doors; 40-5/16 in. on 1-3/8 in. doors
- Used on lighter-duty openings or where the hardware template calls for a narrower prep
E3 -- Deadlock Strike
- Dimensions: 1-1/8 in. wide x 3-1/2 in. tall, 1-1/16 in. deep
- Strike backset: 3/8 in.
- Standard CL: 48 in. from bottom of frame on 1-3/4 in. door
- Used with separate deadbolts -- common in office, healthcare, and retail applications where a deadbolt is specified above the latch
E4 -- Deadlock Strike, No Lip
- Dimensions: 1-1/8 in. wide x 2-3/4 in. tall, 1 in. deep
- Strike backset: 3/8 in.
- Standard CL: 48 in. from bottom of frame
- Used where a lip would conflict with the door edge or frame stop geometry
Electric Strike Preparations: The E9 and What Changes
Electric strikes require a different frame prep than mechanical strikes. The E9 electric strike preparation includes a removable cover box and -- critically -- a 7/8 in. diameter knockout for the electrical connector wiring. Because electric strike bodies vary significantly by manufacturer and model, the frame fabricator must know the specific hardware being used and its required centerline dimension before the frame is ordered.
Key points for specifiers and subs ordering frames with E9 prep:
- Always specify the lock type and centerline dimension when ordering an electric strike prep
- On fire-rated frames, the wallboard must penetrate the throat of the frame by a minimum of 1/2 in., and the electric strike must carry a fire listing for that opening
- Fail-secure electric strikes are the only type permitted on fire-labeled openings -- verify this with your hardware supplier before the frame ships
Preferred electric strike options from brands like Corbin Russwin and Sargent are available at DoorwaysPlus.com and include models engineered to work with standard E9 frame preps without field modification.
Centerline Heights: The Number That Has to Match Across the Schedule
The centerline height -- measured from the bottom of the frame -- controls where the strike opening lands on the jamb. If the frame is fabricated at 40 in. CL and the hardware supplier defaults to a different height, the bolt will not align with the strike.
- Standard latch CL: 40 in. from bottom of frame (1-3/4 in. door), commonly noted as 41 in. AFF in field drawings -- the difference reflects frame reveal vs. finished floor
- Standard deadlock CL: 48 in. from bottom of frame
- Dutch door frames carry additional strike locations; confirm split-rail and upper/lower lock CL dimensions with the frame manufacturer at time of order
On school projects with ADA-driven hardware height requirements, and on healthcare corridor doors where latch and deadbolt function are both specified, verifying CL alignment across the door schedule, frame order, and hardware submittal is a common source of RFIs that can delay a project by weeks.
Strike Prep vs. Soffit Width: A Narrow Frame Problem
On frames with narrow soffit dimensions, the strike reinforcement width defaults to the soffit width rather than the standard 1-1/4 in. This matters when a mortise lock or electric strike with a wider body is specified -- the prep may not provide adequate bearing for the strike screws. Verify hardware compatibility against the frame soffit width before ordering narrow-soffit frames on any opening with a mortise lock function.
Field Cuts: What You Lose When the Prep Does Not Match
When a strike prep does not match the delivered hardware, the fix is usually a field cut -- enlarging or relocating the opening in the frame jamb. This creates several problems:
- The factory reinforcement box is sized for the original prep; cutting outside it means the strike screws may land in thin sheet metal rather than the extruded thread depth
- On fire-rated frames, any modification must conform to the frame's listing requirements -- field cuts without engineer or AHJ sign-off can void the fire label
- On grouted masonry frames, field cuts are far more difficult and may require partial regrouting
The cleanest solution is prevention: build the hardware schedule before the frame order is placed, or at minimum confirm the strike type, CL height, and backset with your hardware supplier before releasing the frame for fabrication.
Practical Checklist: Coordinating Frame Strike Prep With Hardware
- Confirm ANSI strike designation (E1, E2, E3, E4, E9) matches the specified hardware template
- Verify strike backset against door thickness and frame stop configuration
- Confirm centerline height matches the hardware submittal and the door schedule
- Flag electric strike openings early -- specify lock type and CL at time of frame order
- Check fire rating requirements on any opening with an E9 prep; confirm the electric strike is listed for that assembly
- On narrow-soffit frames, verify that the reinforcement width is adequate for the specified strike body
- Coordinate Dutch door, rescue hardware, and non-standard CL frames with the frame manufacturer directly
Get the Right Strike and the Right Prep From DoorwaysPlus
DoorwaysPlus.com carries strikes, electric strikes, and compatible locksets from Sargent, Corbin Russwin, Hager, PDQ, and Accentra -- brands built around stable product lines that do not force full hardware replacements when a component needs service. If you are working through a frame order and need to confirm strike prep compatibility before the fabrication drawing is released, our team can help you match the hardware template to the frame prep before anything ships.