What is a lock backset?

Home security is a crucial concern for every property owner. To ensure the safety of your premises, it is essential to have a good understanding of how door locks work. In this article, we aim to shed light on the topic by answering some frequently asked questions regarding internal and external door locks. One specific component that we will focus on is the lock backset. Although it may not seem like a complex subject, it is crucial to be knowledgeable when it comes to replacing your locks. Stay with us as we delve into the finer details and highlight the key elements that require your attention.

What is a Standard Lock Backset?

In the United Kingdom, carpenters typically use two main backset sizes when working on residential properties: 45 mm and 57 mm. The choice between these sizes depends on whether the door has previously had tubular latches fitted. If you are fitting locks to doors without any prior lock installations, the 57 mm backset size is usually the preferred option. However, if you are replacing existing locks on an old door, it is crucial to ensure that the new lock fits the existing hole.

To determine the backset dimensions of your old lock, measure from the edge of the door to the keyhole or the center of the door knob. Most domestic mortice locks and latches belong to these two main sizes. In imperial measurements, the backset sizes equate to either 2.5″ (44 mm) or 3″ (57 mm). While 60 mm backset locks exist, they are typically found in commercial settings rather than for residential door locks.

Understanding the Backset Size on a Lock

When referring to the backset size, we are talking about the horizontal distance between the edge of the door (the side containing the door stile) and the center of the spindle hole in the lockset. Essentially, the backset size indicates how far the lock is set back from the door’s edge. If you are installing a lock into a new door, measure the appropriate distance from the edge of the door and mark it with a pencil. This principle applies to both door locks and door latches, ensuring that your door handles align properly.

Determining the Right Backset Size

When replacing an old lock, selecting the right size is relatively straightforward, as it is a matter of getting a like-for-like replacement. To measure the existing mortice lock or tubular latch accurately, remove it physically and measure from the faceplate to the square hole (for the spindle) or keyhole. While you could measure from the edge of the door to the existing bored hole, measuring the lock itself provides greater accuracy.

However, when installing new locks in new doors, the conventional wisdom suggests opting for the 57 mm backset. This size positions the door knobs or door handles further away from the frame, preventing the user’s hand from scraping against the door frame or getting painfully caught.

Changing the Backset on an Entry Latch

Sometimes, during door preparation for doorknob installation, you may encounter a misalignment issue with the lock latch hole. Typically, entry latches come in backset sizes of either 57 mm or 44 mm. To ensure proper alignment when installing door knobs, they need to match the backset size. If the latch is not adjustable, you may need to purchase a new one with the right dimensions.

To adjust the latch, you can use needle-nosed pliers. Depending on its age, the latch may be stiff, but with the right tools, the adjustment process should not be too difficult. Align the square hole on both sides of the latch horizontally to form a square shape. Any misalignment will affect the latch’s range of movement, limiting its functionality.

Compatibility of Locks and Doors

In an ideal world, every door knob, lock backset dimension, and mechanism would be universal. However, due to the wide range of door styles, materials, and purposes available, it is crucial to match the right lock to the right use. Different types of doors require specific solutions for operation, security, and aesthetics. For instance, you have:

• 5 Lever Mortice Deadlocks: Most commonly used for wooden external front and back doors, these locks can be locked or unlocked from both sides using a key. Non-BS3621 approved locks often come with a night latch for additional security.
• Multi-Point Lock Systems: Typically fitted with euro cylinder locks, these locks are best suited for external composite and uPVC doors. They can also be found in aluminum and timber doors.
• Rim Automatic Deadlatches: Also known as night latches, these locks are found in glass-paneled doors, as well as timber front and back doors. They are surface-mounted and opened using a rim cylinder with a key. These locks are often combined with a mortice lock for added security.
• Euro Cylinder Locks: A popular option for composite and uPVC doors, these locks can be fitted to sash locks and deadlocks on aluminum or timber doors. While primarily used for external doors, they can also be found internally in hospitals, schools, and offices.

As evident from the examples above, various doors require different lock solutions to ensure operation, security, and aesthetic appeal. Choosing the right lock for your needs depends on the style and function you aim to achieve.

Measure Up, Find the Right Option, and Ensure Success

Selecting the best door lock for any type of door may not be rocket science, but it does require attention to detail. By getting a suitable lock for the job and utilizing adjustable latch features when available, you can ensure a successful installation. We hope this article has provided you with the guidance you need to choose and install the right lock on your first attempt. Thank you for taking the time to read, and we look forward to sharing more valuable insights into other hardware-related topics in the future.