Views: 0 Author: Site Editor Publish Time: 27-02-2025 Origin: Site
In the world of architectural hardware, mortise locks represent the gold standard for security, durability, and aesthetic appeal. Unlike their cylindrical counterparts, mortise locks require a precise pocket—or mortise—to be cut into the door edge, accommodating the lock body. This guide explores the critical dimensions of mortise lock bodies, their standardization, and considerations for proper installation.
The dimensions of mortise lock bodies follow certain industry standards, though variations exist between manufacturers and specific applications. Typically, a standard mortise lock body features:
Length (Backset to Faceplate): The primary dimension ranges from 6 to 7 inches (152-178mm), with 6-1/2 inches (165mm) being the most common in modern residential and commercial applications.
Width (Case Depth): Standard mortise lock bodies measure approximately 4 to 4-1/4 inches (102-108mm) in depth from the door edge to the back of the case.
Height (Case Height): The vertical measurement typically ranges from 3-5/8 to 6 inches (92-152mm), with 4 inches (102mm) being the most common dimension.
Thickness (Case Width): The thickness of the lock body, which determines the width of the mortise pocket, ranges from 15/16 to 1-1/8 inches (24-29mm).
Backset: The distance from the door edge to the center of the cylinder hole typically measures 2-3/4 inches (70mm) in the United States, though European standards often use 65mm or 70mm backsets.
Mortise lock body dimensions vary significantly between regions:
North American Standards: Following ANSI/BHMA A156.13 specifications, American mortise locks typically feature a 4-7/8" (124mm) faceplate height and 1-1/4" (32mm) width.
European Standards: Conforming to DIN 18251 or EN 12209, European mortise locks often use 72mm center distance between the handle and cylinder (known as the "centerline distance"), compared to the 3-3/8" (85.7mm) common in North America.
UK Standards: British standard (BS) mortise locks often feature a 2-1/2" (64mm) or 3" (76mm) backset, with case depths ranging from 2-1/2" to 4" (64-102mm).
Several specialized variants have distinct dimensional requirements:
Narrow Stile Mortise Locks: Designed for aluminum or narrow profile doors, these feature a reduced case depth of approximately 1-1/2" to 2" (38-51mm).
Institutional Mortise Locks: Used in high-security environments, these locks may have reinforced cases up to 1-1/4" (32mm) thick and extended faceplates up to 8" (203mm) in height.
Historical Reproduction Locks: Often feature non-standard dimensions to match antique specifications, with case heights frequently exceeding 6" (152mm) and depths varying substantially.
When selecting and installing mortise locks, several critical dimensional factors deserve attention:
Door Thickness Compatibility: Standard mortise locks accommodate door thicknesses from 1-3/4" to 2" (44-51mm). For thicker or thinner doors, extension kits or custom spindles may be required.
Strike Plate Alignment: The centerline of the lock must align precisely with the strike plate, typically positioned 38-40mm from the door stop.
Edge Distance Requirements: Most mortise locks require a minimum edge distance of 1/2" (13mm) from the lock centerline to the edge of the door stile to maintain structural integrity.
Minimum Stile Width: For proper installation, the door stile should be at least 4-1/2" (114mm) wide to accommodate the lock body without compromising door strength.
Contemporary mortise lock designs have evolved to address changing architectural requirements:
Thin Door Adaptations: Modified lock bodies with reduced case depths of 3-1/2" (89mm) or less accommodate thinner door profiles in modern construction.
Electronic Integration: Smart mortise locks often feature slightly larger case dimensions—typically 1/4" (6mm) wider—to accommodate electronic components while maintaining compatibility with standard door preparations.
Adjustable Backsets: Some innovative designs offer adjustable backsets that can shift from 2-3/4" to 2-3/8" (70mm to 60mm) to accommodate different door specifications.
Understanding mortise lock body dimensions is essential for architects, contractors, and hardware specifiers. These precise measurements ensure proper fit, functionality, and security performance. While standardization exists within regions, awareness of dimensional variations between manufacturers and international standards is crucial when specifying mortise hardware, particularly in renovation projects or when sourcing components from different markets. Proper attention to these dimensional details will result in smoother installation, better operation, and longer lock service life.
