Deadlock, Deadbolt or Sash Lock: Which Do You Need?


Last Reviewed: 17 September 2026

This post is part of our regularly reviewed content series, ensuring all advice remains accurate and relevant to your home project.

Author: Carl Benson

Carl is the founder of Suffolk Latch Company, with a background in engineering and over 20 years’ experience in home hardware. He works closely with suppliers and designers to develop quality ironmongery that stands the test of time. Read my full bio.

Carl Benson

Introduction

Deadlocks, deadbolts and sash locks are all fitted into the edge of a door, but they perform different functions. A deadlock provides key-operated locking, a bathroom deadbolt provides privacy using a thumbturn, and a sash lock combines a latch and locking bolt within one case.

Choosing the correct mechanism depends on whether the door needs to latch during everyday use, lock with a key, provide bathroom privacy or form part of the security for an external entrance.

This guide explains each option, the measurements to check and the difference between internal privacy hardware and an appropriate external-door security lock.

Table of Contents

  1. Deadlock, Deadbolt and Sash Lock: Quick Comparison
  2. What Is a Mortice Deadlock?
  3. Three-Lever and Five-Lever Deadlocks
  4. What Is a Bathroom Deadbolt?
  5. What Is a Mortice Sash Lock?
  6. Euro Profile Sash Locks
  7. Bathroom Sash Locks
  8. Measurements to Check Before Ordering
  9. Which Lock Should You Choose?
  10. FAQ

Deadlock, Deadbolt and Sash Lock: Quick Comparison

  • Mortice deadlock: A key-operated locking bolt without a latch. It does not operate a door handle or knob.
  • Bathroom deadbolt: A privacy bolt operated by a compatible bathroom turn and release rather than a conventional key.
  • Mortice sash lock: Combines a sprung latch for the handle with a separate locking bolt in one case.
  • Bathroom sash lock: Combines a handle-operated latch with a privacy bolt operated by a bathroom turn and release.
  • Euro profile sash lock: Combines a latch and locking bolt but uses a separate Euro profile cylinder.

If you need a broader overview, browse our complete collection of door latches and locks.

Traditional mortice deadlock and key illustration

What Is a Mortice Deadlock?

A mortice deadlock is recessed into a pocket cut into the edge of a timber door. Turning the key projects the locking bolt into a strike plate fitted to the door frame.

A deadlock contains no sprung latch. It therefore does not hold the door closed during normal use and is not operated by a door handle or knob. If the door also needs to latch, it will require a separate latch, night latch or another suitable closing mechanism.

Deadlocks are useful where key-operated locking is required independently of the door furniture. Browse our mortice deadlocks.

Three-Lever and Five-Lever Deadlocks

Three-Lever Deadlocks

Three-lever deadlocks are generally used on internal timber doors where key-operated privacy or restricted access is required. Examples might include a study, store room or home office.

They should not be assumed to provide the security required for an external entrance door.

Three-inch mortice deadlock drawing

Five-Lever Deadlocks

Five-lever deadlocks are commonly associated with timber entrance doors, but the number of levers alone does not confirm the security level of a particular lock.

For an external door, check the lock’s current certification, the type and condition of the door, the required level of protection and any conditions imposed by your home insurer. Look for the relevant certification marking on the specific product rather than relying solely on its description as a five-lever lock.

If you are uncertain, ask a qualified locksmith to assess the complete door and frame.

What Is a Bathroom Deadbolt?

A bathroom deadbolt is a simple privacy mechanism morticed into the edge of an internal door. Instead of being operated by a key, it is controlled by a compatible bathroom turn and release.

The thumbturn on the inside projects the bolt into the strike plate. The release on the outside usually provides a way to unlock the door in an emergency.

A deadbolt does not operate the door knob or handle. If the door must also latch closed, it normally needs a separate tubular latch.

This separate arrangement gives greater flexibility over the vertical position of the turn and release. It can be particularly useful when fitting traditional door knobs.

Three-inch bathroom deadbolt drawing with measurements

Beehive door knob, bathroom deadbolt and turn and release set

Browse our tubular latches and bathroom deadbolts.

What Is a Mortice Sash Lock?

A mortice sash lock combines two mechanisms within a single case:

  • A sprung latch operated by a door handle or compatible door knob
  • A separate locking bolt operated by a key

This allows the door to latch closed during everyday use and then be locked when required. A sash lock is therefore a practical choice when you want a lever handle and key-operated lock to work together.

Three-inch three-lever mortice sash lock

Three-Lever Sash Locks

A three-lever sash lock is generally used on internal doors that require both a handle-operated latch and key-operated locking.

Five-Lever Sash Locks

Five-lever sash locks are commonly fitted to timber entrance doors where a lever handle and key-operated lock are required.

For an external entrance, confirm that the particular lock carries the appropriate current certification and meets your insurer’s requirements. Do not rely on the number of levers alone.

Two-and-a-half-inch five-lever sash lock drawing

Five-lever sash lock fitted with a lever door handle

Browse our current collection of mortice sash locks.

Euro Profile Sash Locks

A Euro profile sash lock also contains a latch and locking bolt, but the lock is operated by a separate Euro profile cylinder rather than a traditional lever key.

One advantage of a cylinder-operated system is that the cylinder can often be replaced without changing the complete lock case. This may be useful if the keys are lost or access arrangements change.

The cylinder and sash lock must be compatible. The cylinder length should also suit the combined thickness of the door and any escutcheons or security furniture without projecting excessively.

For an external entrance door, choose the complete locking arrangement according to the door construction, security requirements and any insurer conditions.

Two-and-a-half-inch Euro profile sash lock drawing

Bathroom Sash Locks

A bathroom sash lock combines a sprung latch and privacy bolt within one case. The latch is operated by the door handle, while a separate bathroom turn and release operates the locking bolt.

This arrangement keeps the visible door furniture neatly aligned on one backplate or within one coordinated handle set. It is commonly used with lever handles.

Bathroom sash locks provide privacy rather than external-door security. The outside release allows assistance to be provided if someone is unable to unlock the door from inside.

Two-and-a-half-inch bathroom sash lock drawing

Measurements to Check Before Ordering

Lock dimensions vary, even when two products have similar descriptions. Check the technical drawing for the exact product before cutting or altering the door.

Case Depth

The case depth is measured from the front edge of the forend to the back of the lock body. Nominal sizes such as 2.5 inches and 3 inches usually refer to the case depth.

Backset

The backset is the distance from the edge of the door to the centre of the handle spindle, keyhole, thumbturn or cylinder, depending on the mechanism.

A deeper backset positions the handle, knob or keyhole further from the door frame. This can improve hand clearance when using door knobs.

Centres

On a sash lock, the centres measurement is the vertical distance between the centre of the handle spindle and the centre of the keyhole, thumbturn spindle or cylinder.

The lock centres must match the centres of the selected backplate handle or other door furniture.

Door Thickness and Existing Cut-Outs

Check that the door is thick enough to contain the lock case safely. If you are replacing an existing mechanism, compare the new case, forend, backset and centres with the original cut-out.

Particular care is required with panelled, glazed and fire doors. Do not cut into a fire door unless the selected hardware and installation method are compatible with the certified door assembly.

Which Lock Should You Choose?

  • Internal door requiring key-operated locking but no handle-operated latch: Consider a suitable three-lever deadlock.
  • Internal door requiring a lever handle and key: Consider a suitable three-lever sash lock.
  • Bathroom fitted with separate door knobs: A tubular latch and separate bathroom deadbolt may provide the most flexible arrangement.
  • Bathroom fitted with lever handles: A compatible bathroom sash lock and turn and release may be suitable.
  • External timber entrance door: Choose a properly certified lock or locking system that suits the door and satisfies any insurance requirements.
  • Door using a Euro cylinder: Select a compatible Euro profile lock and correctly sized cylinder.

For a wider comparison, read our guide: Which Lock or Latch Do You Need?

FAQ

What is the difference between a deadlock and a deadbolt?

A mortice deadlock is normally operated by a key and contains a locking bolt without a latch. A bathroom deadbolt is normally operated by a compatible thumbturn and provides privacy on an internal door.

What is the difference between a deadlock and a sash lock?

A deadlock contains only a locking bolt. A sash lock contains both a sprung latch for a handle and a separate locking bolt.

Can a deadlock be used with a door handle?

A deadlock does not operate a handle. If the same door needs a handle-operated latch, it will require a separate latch or a sash lock containing both mechanisms.

Do I need a deadbolt or bathroom sash lock?

A separate bathroom deadbolt is useful when the privacy control needs to be positioned independently of the latch, often with door knobs. A bathroom sash lock combines the latch and privacy bolt and is commonly paired with lever handles.

Is every five-lever lock suitable for an external door?

No. Lever count alone does not confirm the security rating. Check the particular lock’s certification, its compatibility with the door and any requirements set by your insurer.

What is the backset on a door lock?

The backset is the distance from the edge of the door to the centre of the spindle, keyhole, thumbturn or cylinder. Check the technical drawing because the relevant centre depends on the lock type.

Can I fit a mortice lock myself?

Morticing requires accurate cutting and alignment. Incorrect installation can weaken the door or prevent the lock from working properly. Ask an experienced joiner or locksmith if you are unsure, particularly for external, glazed or fire doors.

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