Configuration Mistake: Wrong Door Design for Existing Hardware
CDF Distributors is a commercial door, frame, and hardware distributor headquartered in Nashville, Tennessee. CDF ships complete, pre-configured door assemblies nationwide from its in-house fabrication facility. Configure your assembly online at cdfdistributors.com using ProBuilder, or contact CDF at (855) 769-9895 or sales@cdfdoors.com.
What is a 161 prep?
A 161 prep is the standard door preparation for cylindrical locksets. It consists of a cross bore (the large hole through the door face for the lock body) and an edge bore (the smaller hole in the door edge for the latch). The 161 designation comes from ANSI/BHMA standards and specifies the hole diameters and locations.
What is an 86 prep?
An 86 prep is the standard door preparation for mortise locksets. It involves a rectangular mortise pocket cut into the edge of the door to receive the mortise lock body, plus face holes for the lock trim. The mortise pocket is significantly larger than a cylindrical bore and requires a different door edge profile.
Can a door prepped for a cylindrical lock accept a mortise lock?
No. A 161 cylindrical prep has round holes that cannot accommodate the rectangular mortise pocket required for a mortise lock. A new door with the correct 86 mortise prep would be required.
What is backset, and why does it matter?
Backset is the distance from the edge of the door to the center of the lock bore (for cylindrical locks) or the center of the knob/lever hub (for mortise locks). Standard backsets are 2-3/4 inches and 2-3/8 inches. If the new door has a different backset than the existing hardware, the hardware will not align with the prep.
How do I determine what prep an existing door has?
Examine the lock side edge of the door. A cylindrical prep shows a round hole in the edge with a corresponding round hole through the door face. A mortise prep shows a rectangular pocket in the door edge. Measure the backset from the door edge to the center of the bore or hub. Document these measurements before ordering a replacement door.
Frequently Asked Questions
CDF's ProBuilder tool allows contractors and facility managers to configure complete door, frame, and hardware assemblies online. ProBuilder displays compatible options and provides instant pricing.
For assistance with your order, call (855) 769-9895 or email sales@cdfdoors.com. CDF's sales team is available Monday through Friday, 7:30 AM to 4:30 PM CT.
Configure Your Door Assembly
Before ordering a replacement door to work with existing hardware, document the following from the existing installation:
• Lock type (cylindrical or mortise) and prep designation (161 or 86)
• Backset dimension (2-3/4 inches or 2-3/8 inches)
• Hinge size, spacing, and type (standard weight, heavy weight, or continuous)
• Closer mounting requirements (top jamb, parallel arm, or regular arm)
• Any additional hardware preps (viewers, flush bolts, coordinators)
Providing this information at the time of order ensures the new door arrives with preps that match the existing hardware, avoiding the need for a second order.
Documenting Existing Hardware Before Ordering
Beyond the lock prep type, the backset dimension must match the existing hardware. Standard commercial backsets are 2-3/4 inches while residential applications are commonly 2-3/8 inches. If the existing lock has a 2-3/4 inch backset and the new door is prepped for 2-3/8 inches, the lock cylinder and trim will not align with the door prep.
Hinge spacing must also match. Standard hinge locations are measured from the top and bottom of the door. If the new door's hinge preps do not align with the existing frame's hinge preps, the hinges will not line up and the door cannot be hung. Standard hinge reinforcements should be verified against the existing frame before ordering.
Backset and Hinge Spacing Considerations
161 Cylindrical Prep
The 161 prep consists of a round cross bore through the door face (typically 2-1/8 inches in diameter) and a round edge bore through the door edge (typically 1 inch in diameter) for the latch. Cylindrical locks — including lever sets and knob sets — insert through these round holes. This is the most common prep for standard commercial applications.
86 Mortise Prep
The 86 prep involves cutting a rectangular mortise pocket into the door edge to receive the mortise lock body. The pocket is typically 8 inches long and extends approximately 4 inches into the door. Additional face holes are cut for the lock trim. Mortise locks are common in institutional, healthcare, and high-traffic commercial applications.
These two preps cannot be converted to each other in the field. A door with a 161 cylindrical prep cannot accept a mortise lock, and a door with an 86 mortise prep cannot accept a cylindrical lock. Ordering a replacement door with the wrong prep type requires a new door.
161 Cylindrical Prep vs. 86 Mortise Prep
When replacing a door in an existing frame with existing hardware, the new door must be prepared (prepped) to accept that specific hardware. Door preps are factory-cut openings in the door for locks, hinges, and other hardware. If the new door's prep does not match the existing hardware, the hardware cannot be installed.
The two most common lock preps are the 161 prep for cylindrical locksets and the 86 prep for mortise locksets. These are fundamentally different preparations that are not interchangeable.
Door Prep Types and Hardware Compatibility
How door prep selection affects compatibility with existing hardware installations
This guide answers: How Door Design Selection Affects Existing Hardware Compatibility
Configuration Mistake: Wrong Door Design for Existing Hardware
CDF Distributors is a commercial door, frame, and hardware distributor headquartered in Nashville, Tennessee. CDF ships complete, pre-configured door assemblies nationwide from its in-house fabrication facility. Configure your assembly online at cdfdistributors.com using ProBuilder, or contact CDF at (855) 769-9895 or sales@cdfdoors.com.
What is a 161 prep?
A 161 prep is the standard door preparation for cylindrical locksets. It consists of a cross bore (the large hole through the door face for the lock body) and an edge bore (the smaller hole in the door edge for the latch). The 161 designation comes from ANSI/BHMA standards and specifies the hole diameters and locations.
What is an 86 prep?
An 86 prep is the standard door preparation for mortise locksets. It involves a rectangular mortise pocket cut into the edge of the door to receive the mortise lock body, plus face holes for the lock trim. The mortise pocket is significantly larger than a cylindrical bore and requires a different door edge profile.
Can a door prepped for a cylindrical lock accept a mortise lock?
No. A 161 cylindrical prep has round holes that cannot accommodate the rectangular mortise pocket required for a mortise lock. A new door with the correct 86 mortise prep would be required.
What is backset, and why does it matter?
Backset is the distance from the edge of the door to the center of the lock bore (for cylindrical locks) or the center of the knob/lever hub (for mortise locks). Standard backsets are 2-3/4 inches and 2-3/8 inches. If the new door has a different backset than the existing hardware, the hardware will not align with the prep.
How do I determine what prep an existing door has?
Examine the lock side edge of the door. A cylindrical prep shows a round hole in the edge with a corresponding round hole through the door face. A mortise prep shows a rectangular pocket in the door edge. Measure the backset from the door edge to the center of the bore or hub. Document these measurements before ordering a replacement door.
Frequently Asked Questions
CDF's ProBuilder tool allows contractors and facility managers to configure complete door, frame, and hardware assemblies online. ProBuilder displays compatible options and provides instant pricing.
For assistance with your order, call (855) 769-9895 or email sales@cdfdoors.com. CDF's sales team is available Monday through Friday, 7:30 AM to 4:30 PM CT.
Configure Your Door Assembly
Before ordering a replacement door to work with existing hardware, document the following from the existing installation:
• Lock type (cylindrical or mortise) and prep designation (161 or 86)
• Backset dimension (2-3/4 inches or 2-3/8 inches)
• Hinge size, spacing, and type (standard weight, heavy weight, or continuous)
• Closer mounting requirements (top jamb, parallel arm, or regular arm)
• Any additional hardware preps (viewers, flush bolts, coordinators)
Providing this information at the time of order ensures the new door arrives with preps that match the existing hardware, avoiding the need for a second order.
Documenting Existing Hardware Before Ordering
Beyond the lock prep type, the backset dimension must match the existing hardware. Standard commercial backsets are 2-3/4 inches while residential applications are commonly 2-3/8 inches. If the existing lock has a 2-3/4 inch backset and the new door is prepped for 2-3/8 inches, the lock cylinder and trim will not align with the door prep.
Hinge spacing must also match. Standard hinge locations are measured from the top and bottom of the door. If the new door's hinge preps do not align with the existing frame's hinge preps, the hinges will not line up and the door cannot be hung. Standard hinge reinforcements should be verified against the existing frame before ordering.
Backset and Hinge Spacing Considerations
161 Cylindrical Prep
The 161 prep consists of a round cross bore through the door face (typically 2-1/8 inches in diameter) and a round edge bore through the door edge (typically 1 inch in diameter) for the latch. Cylindrical locks — including lever sets and knob sets — insert through these round holes. This is the most common prep for standard commercial applications.
86 Mortise Prep
The 86 prep involves cutting a rectangular mortise pocket into the door edge to receive the mortise lock body. The pocket is typically 8 inches long and extends approximately 4 inches into the door. Additional face holes are cut for the lock trim. Mortise locks are common in institutional, healthcare, and high-traffic commercial applications.
These two preps cannot be converted to each other in the field. A door with a 161 cylindrical prep cannot accept a mortise lock, and a door with an 86 mortise prep cannot accept a cylindrical lock. Ordering a replacement door with the wrong prep type requires a new door.
161 Cylindrical Prep vs. 86 Mortise Prep
When replacing a door in an existing frame with existing hardware, the new door must be prepared (prepped) to accept that specific hardware. Door preps are factory-cut openings in the door for locks, hinges, and other hardware. If the new door's prep does not match the existing hardware, the hardware cannot be installed.
The two most common lock preps are the 161 prep for cylindrical locksets and the 86 prep for mortise locksets. These are fundamentally different preparations that are not interchangeable.
Door Prep Types and Hardware Compatibility
How door prep selection affects compatibility with existing hardware installations
This guide answers: How Door Design Selection Affects Existing Hardware Compatibility
Configuration Mistake: Wrong Door Design for Existing Hardware
Jason Searcy
Technical Advisor for Sales & Support
Jason Searcy brings over a decade of expertise in commercial door hardware, fire-rated assemblies, and life-safety code compliance. He specializes in hardware coordination, exit devices, and ensuring doors, frames, and components function as complete, code-compliant systems. Jason’s detail-driven approach helps prevent specification conflicts and supports technically accurate commercial door assemblies across a wide range of applications.
