Hardware Prep Basics: What Contractors Need to Know Before Ordering

Why Hardware Preps Must Be Specified at Order Time

Unlike a wood door that a carpenter can modify in the field, hollow metal doors are machined at the factory. Every cutout, reinforcing plate, and tapped hole for hardware is produced during manufacturing — before the door ships. This means that if you order the wrong prep, or forget a prep entirely, correcting the error in the field is difficult, expensive, and sometimes structurally inadvisable.

A properly prepped door arrives at the job site ready for the hardware installer to drop in and torque down. An incorrectly prepped door creates delays, additional costs, and in some cases requires a replacement door. Getting the preps right at the time of order is one of the highest-value steps in the hollow metal procurement process.

Hinge Prep

The most universal prep on any hollow metal door is the hinge prep. Standard hollow metal doors are prepared for full-mortise hinges per ANSI/BHMA A156.7. The standard hinge size for commercial hollow metal is 4-1/2" x 4-1/2", though 5" x 4-1/2" and other sizes are available for heavy doors or specific hinge products.

Standard hinge locations on a 7'0" door are:

• Top hinge: 5" from the top of the door to the top of the hinge cutout
• Bottom hinge: 10" from the bottom of the door to the bottom of the hinge cutout
• Intermediate hinge: 60" from the bottom of the door (center of hinge)

Three hinges are standard for most commercial doors up to 7'6" and 200 lbs. Specify four hinges for doors over 7'6", over 200 lbs., or when the hardware schedule or spec calls for four. Always confirm the hinge count with the hardware set before ordering.

Lock Prep

Lock preps are defined by ANSI prep templates that specify the exact cutout geometry, backset, and reinforcing for different lock types. The most common preps for commercial hollow metal doors are:

• ANSI 161 — The standard prep for cylindrical locks (latchbolts and deadbolts). Most commercial locksets use this prep. Standard backset is 2-3/4" (some applications use 3-3/4").
• ANSI 86 — The standard prep for mortise locksets, which require a deeper pocket cut into the door edge. Mortise locks are common in higher-security commercial applications.
• ANSI 115 / 115W — Preps for deadbolts and auxiliary locks above or below the primary lock.

When specifying lock prep, identify the lock type (cylindrical or mortise), the ANSI prep number, the backset, and the hand of the door. Your hardware schedule should contain all of this information by opening number.

Closer Prep

Door closers are surface-mounted to the door and/or frame and require reinforcing plates factory-installed at the closer mounting location. Specify the closer prep based on the mounting method:

• Regular arm (top rail mount) — Closer body mounts to the door's top rail. Reinforcing plate is installed inside the top rail of the door.
• Parallel arm (pull side) — Closer body mounts to the frame head; the arm connects to the door's top rail. Reinforcing is required at the door and at the frame head.
• Track arm / slide arm — Used where the door swings nearly 180 degrees. Requires specific door and frame reinforcing.

If you know the closer brand and model number, provide it. Different closer manufacturers have slightly different mounting hole patterns, and specifying by manufacturer ensures the reinforcing matches the product being installed.

Other Common Preps

Beyond hinges, locks, and closers, hollow metal doors can be prepped for a variety of other hardware items at the factory:

• Flush bolts — Used on the inactive leaf of a pair of doors. Top and bottom flush bolt preps are cut into the door edge and face.
• Strike preps — The door frame is prepped for the strike plate that receives the latchbolt or deadbolt. Strike geometry must match the lock prep.
• Silencer holes — Small holes drilled in the frame stop to receive rubber door silencers. Typically 3 per single door (top, middle, bottom of the strike jamb stop).
• Viewer (peephole) prep — A through-hole at a specified height for door viewers, common in residential-adjacent or hospitality applications.
• Surface bolt prep — Similar to flush bolt but surface-mounted; requires only a strike location on the frame or floor.

Through-Bolted vs. Tapped Preps

Hardware reinforcing in hollow metal doors can be either through-bolted or tapped (threaded), and the hardware being installed determines which is appropriate:

• Through-bolted — Hardware bolts pass completely through the door to a nut and washer on the opposite face. Used for closers, concealed overhead stops, and other hardware where bolt-through attachment is specified by the hardware manufacturer. Provides the highest pull-out resistance.
• Tapped — Hardware screws thread directly into tapped holes in the reinforcing plate. Used for most surface-applied hardware including locks, flush bolts, and push/pull plates. Faster installation but relies on the quality of the thread engagement.

Confirm the attachment method for each hardware item with the hardware supplier before specifying preps. Mismatched attachment methods can result in hardware that won't mount correctly or fails under load.