Door Locks Explained: 3 Lever vs 5 Lever Sash Locks

What Is a Sash Lock?

A sash lock is sometimes called a mortice sash lock. It contains both a deadbolt and latch within a single case.

Sash locks are fitted into the edge of a door rather than onto the surface. They are designed to work with a pair of door handles, with the deadbolt operated by a key from either side of the door.

3 Lever Locks

Three-lever sash locks are designed for internal doors in domestic properties. They are best suited to doors that need to be locked for privacy, rather than high-security purposes.

Because they have fewer levers, key duplication is generally easier than with a five-lever lock. Three-lever locks are ideal for bedrooms, studies and internal rooms that need to be closed off from the rest of the house.

These locks can be used on standard internal wooden doors.

Three-lever locks are generally available in two standard case depths: 2.5 inches (64mm) and 3 inches (76mm).

When choosing the correct size of three-lever lock, consider the following:

• Is your door thick enough to accommodate a three-lever lock? Standard doors are usually 35mm to 40mm thick, while internal fire doors are often between 35mm and 54mm.
• Where do you want to fit your handle? You will need to measure the backset, which is the distance between the edge of the door and the centre of the spindle hole. The backset of a 2.5-inch sash lock is 44mm, while the backset of a 3-inch sash lock is 57mm.

These door locks have striker plates and face plates available in different finishes to match your door handles and door knobs. Browse our range of 3 lever locks.

5 Lever Locks

Five-lever sash locks are most commonly used for external doors. The additional levers provide a higher level of security than a three-lever lock.

When choosing a five-lever lock for an external door, check that it is stamped or kitemarked to BS3621. This British Standard applies to thief-resistant locks and is often required by home insurance providers.

Five-lever locks are also generally sold in two case sizes: 2.5 inches and 3 inches. These usually translate to backset measurements of 44mm and 57mm.

When choosing the correct size for your external door, consider the following:

• The thickness of your door.
• The backset measurement from the edge of the door to the centre of your door handle.
• If you have existing handles, check that the centres measurement matches your five-lever lock. This is the vertical measurement between the centre of the keyhole and the centre of the spindle hole.

Browse our selection of 5 lever locks.

Related Articles

You may also find these guides useful:

• Unboxing Your Door Knobs Guide
• How to Fit a Tubular Latch
• Door Knobs vs Door Handles: How to Choose