What This Article Covers -- and Who It Helps
Drilling a wood door for a cylindrical lockset looks straightforward until the latch binds, the rose gaps, or the lock case pulls loose from undersized blocking. This guide walks through every preparation dimension that determines whether a bored lockset installs cleanly and operates reliably -- useful for commercial finish carpenters, hardware subcontractors, school facilities crews doing in-house replacements, and anyone specifying pre-machined doors on a project schedule.
What Is a Cylindrical Lockset Prep?
A cylindrical lockset prep (also called a bored lock prep) is the set of holes and mortises cut into a door that allow a cylindrical lock body to seat correctly. Unlike a mortise lock -- which requires a deep pocket routed into the door edge -- a cylindrical lock uses two intersecting bores: a large-diameter cross bore through the door face and a smaller edge bore into the door stile. The lock case snaps into the cross bore; the latch assembly slides into the edge bore.
Getting these dimensions right before the drill touches wood is the difference between a clean install and a callback.
The Four Dimensions That Drive Every Wood Door Prep
1. Cross Bore Diameter
The large face hole is almost always 2-1/8 inches (54 mm) in diameter for standard commercial cylindrical locksets. Some heavy-duty or oversized chassis -- such as certain Grade 1 lever locks -- may use a 3-1/8 inch (79.4 mm) cross bore; always verify against the manufacturer template before drilling. Corbin Russwin CK4300 Series hardware, for example, specifies a 3-1/8 inch cross bore, while the CK4800 Series uses 2-1/8 inches. Accentra (formerly Yale) 4600 and 5300 series lever and knob locks call for 2-1/8 inches as standard.
Key field rule: To avoid splintering on wood doors, drill from both faces toward the center -- never push the hole saw through in one pass.
2. Edge Bore Diameter and Depth
The edge bore accepts the latch assembly. Standard diameter is 1 inch (25 mm). The mortise for the latch front (the flat faceplate on the door edge) is typically 1-1/8 inches (29 mm) wide by approximately 2-1/4 inches (57 mm) tall, recessed 5/32 inch (4 mm) deep -- enough so the front sits flush with the door edge surface.
Some latch models ship with a 1/8-inch sleeve to accommodate doors prepped with a 1-inch bore where a slightly smaller latch body is used. Check the latch specification table before ordering pre-machined doors.
3. Backset
Backset is measured from the centerline of the door bevel (the door edge centerpoint) to the center of the cross bore. The two standard commercial backsets are:
- 2-3/8 inches (60 mm) -- used on narrower stiles and some retrofit situations
- 2-3/4 inches (70 mm) -- the ANSI/BHMA A156.115W standard backset for wood doors, and the most common spec on new commercial construction
Extended backsets of 3-3/4 inches (95 mm), 5 inches (127 mm), and 6 inches (152 mm) exist for wide-stile applications. A prior post on this site covers the 2-3/4 vs. 2-3/8 decision in detail; this article focuses on the full preparation sequence rather than that single dimension choice.
4. Through-Bolt Hole Locations
Most commercial cylindrical locksets are secured with two 5/16-inch (8 mm) through bolts that pass from the inside rose assembly through the door to the outside trim. Template documents from manufacturers such as Accentra and Corbin Russwin specify exact centerline locations for these holes relative to the cross bore center. Do not estimate -- use the printed template every time.
Latch Front: Square, Radius, or Drive-In?
The latch front shape must match the door prep mortise:
- Square corner front -- requires a square-cornered mortise; most common on commercial wood doors
- Radius corner front (round) -- easier to cut cleanly with a router; common on hollow-core doors and light commercial
- Drive-in latch -- no mortise required; the latch clips into the edge bore; used on some light-duty applications
Specify latch front type on the hardware schedule and confirm the pre-machined door order matches. A square-front latch will rock in a radius mortise and telegraph through the rose.
Door Thickness and Bevel Tolerance
Standard commercial wood doors run 1-3/4 inches (44 mm) thick. Some cylindrical locksets will also accommodate 1-3/8-inch (35 mm) doors with spacers under the rose assemblies -- verify with the lock manufacturer before specifying on hollow-core or lightweight interior doors.
Wood doors are beveled at the latch edge: 1/8 inch per 2 inches of door thickness (approximately 3.2 mm per 50.8 mm). Backset is always measured to the centerline of the bevel, which is the centerpoint of the door thickness -- not the face or the arris edge. Misreading this adds error to every downstream dimension.
Fire-Rated Wood Doors: What Changes
If the opening carries a fire rating, the door prep must comply with NFPA 80 and the door manufacturer's label service requirements. Key restrictions for fire-rated wood doors:
- Field preparation beyond what is listed is not permitted without label service authorization
- Surface-applied hardware holes are limited to a maximum of 1 inch in diameter; cylinder holes are exempt from this limit
- Maximum undercut for wood and composite fire doors is 3/4 inch
- All lock hardware on a fire door assembly must be listed for the applicable fire rating period
If the door arrives from the factory pre-machined to the correct ANSI prep, no additional field boring is needed -- and that is the preferred approach on labeled assemblies.
Electrified Cylindrical Locksets: Add a Wire Raceway Step
When the schedule calls for an electrified cylindrical lockset -- common in healthcare nurse stations, school secured vestibules, and retail back-of-house access control -- the wood door must include a wire raceway from the lock prep location to the hinge edge of the door. Templates for electrified versions, such as Corbin Russwin CL33900 and Accentra 5400LN solenoid-controlled series, call for a 3/8-inch (9.5 mm) minimum raceway routed by the door manufacturer. This cannot be added cleanly in the field after the door is hung. Coordinate the raceway requirement with the door supplier before the door ships.
Preferred Lock Lines for Wood Door Applications
When specifying cylindrical locksets for wood doors across school, healthcare, retail, and light industrial openings, DoorwaysPlus stocks and recommends Grade 1 lines from Corbin Russwin, Accentra (formerly Yale), Sargent, Hager, and PDQ. These lines publish clear template documentation, offer both 2-3/8 and 2-3/4 backset configurations, and carry consistent ANSI/BHMA Grade 1 listings -- making the prep-to-installation sequence predictable across a project schedule.
Quick Prep Checklist Before You Drill
- Confirm cross bore diameter from the lock manufacturer template -- 2-1/8" vs. 3-1/8" matters
- Confirm backset: 2-3/4" standard, 2-3/8" only when stile or existing prep requires it
- Confirm latch front style matches the mortise you will cut
- Mark through-bolt locations from the printed template -- do not scale
- Drill cross bore from both faces on wood to prevent blowout
- Check door thickness; add spacers if under 1-3/4"
- On electrified units, confirm raceway is in the door before it leaves the shop
- On fire-rated doors, verify the prep is within label service limits before any field modification
Get the Right Lock and the Right Prep Dimensions from DoorwaysPlus
DoorwaysPlus carries cylindrical locksets, template documentation, and application support for wood door openings across every commercial sector. Whether you are specifying a school corridor, a clinic exam room, or an industrial employee entrance, the right prep starts with the right information. Visit DoorwaysPlus.com to shop cylindrical locksets or contact our team for help matching lock specs to your door schedule.