Security Locks – Roundtower Hardware

Choosing the Right Security Lock

The correct door security lock will depend on where the door is located, the level of security required and how you want the door to operate.

For external entrance doors, a properly tested security lock should be selected rather than assuming that every mortice lock provides the same level of protection.

Within our range, the principal choices are 5 lever sashlocks, 5 lever deadlocks and 3 lever mortice locks in 2½" and 3" case sizes.

5 Lever Mortice Locks

A 5 lever mortice lock uses five internal levers that must be correctly aligned by the key before the deadbolt can operate.

5 lever locks are commonly selected for entrance doors where a higher level of security is required.

Our Atlantic 5 lever mortice locks are available in both sashlock and deadlock configurations, with selected models tested to BS 3621.

When security standards or insurance requirements apply, always check the exact certification of the individual lock rather than relying simply on the number of levers.

What is BS 3621?

BS 3621 is a recognised standard for key-operated thief-resistant locks used on doors.

A lock marked as complying with BS 3621 has undergone defined security and performance testing.

If an insurance policy or project specification requires a BS 3621 lock, ensure that the exact product being installed carries the appropriate certification.

Sashlock or Deadlock?

A mortice sashlock combines two functions within one lock case.

The spring latch holds the door closed during normal use and is operated by a lever handle or compatible door knob. A separate deadbolt is operated by the key to lock the door.

A mortice deadlock contains the locking deadbolt but does not include a spring latch.

Deadlocks can therefore be used where a separate latch is not required or as an additional locking point on a suitable door.

3 Lever vs 5 Lever Locks

The main difference is the number of internal levers used by the locking mechanism.

A 3 lever lock is generally intended for applications where a lower level of security is acceptable, such as appropriate internal doors.

A 5 lever security lock provides a higher level of key security and is more commonly selected for entrance doors.

However, the number of levers should not be considered in isolation. Where security performance matters, the relevant standard and certification of the complete lock are more important.

2½" or 3" Mortice Lock?

Mortice locks within our range are available in 2½" and 3" case sizes.

The case size affects the position of the keyhole and handle relative to the edge of the door.

A deeper 3" lock positions the operating furniture further from the door edge, which can be useful with larger door knobs or where additional hand clearance from the frame is preferred.

When replacing an existing lock, measure the existing case and backset before ordering.

What is the Backset?

The backset is the distance from the edge of the door or lock faceplate to the centre of the keyhole, spindle or cylinder position.

It is an important measurement when replacing an existing mortice lock because changing the backset will alter the position of the door furniture.

Checking the backset, case depth and faceplate dimensions can make it much easier to identify a suitable replacement.

Matching Locks with Door Furniture

Mortice locks should be selected together with the door handles, knobs and escutcheons that will operate them.

A sashlock requires compatible lever handles or mortice knobs to operate the latch, together with suitable keyhole furniture.

A deadlock does not require a lever handle to operate the lock itself, although the door may have separate pull or other door furniture depending on the application.

Choosing coordinated lock faceplates and architectural finishes can also create a more consistent door specification.

Frequently Asked Questions

What is a 5 lever security lock?

A 5 lever lock contains five internal levers that must align correctly before the key can operate the deadbolt.

For security-critical applications, look for the relevant tested standard such as BS 3621 rather than judging the lock solely by the number of levers.

Are 5 lever locks suitable for front doors?

Selected 5 lever locks are specifically designed for external entrance doors.

Where a particular security or insurance standard is required, check that the individual lock carries the necessary certification.

What is the difference between a sashlock and deadlock?

A sashlock contains both a latch and deadbolt, allowing the door to operate with a handle and also be locked with a key.

A deadlock contains only the locking bolt and does not include the spring latch used for everyday door operation.

Is a 3 lever lock a security lock?

A 3 lever lock provides key-operated locking, but it should not automatically be treated as equivalent to a higher-security 5 lever lock tested to a recognised security standard.

Three-lever locks are generally more appropriate for internal or less security-critical applications.

What does BS 3621 mean?

BS 3621 is a security standard for key-operated thief-resistant locks.

If your insurance company or specification requires BS 3621, check that the exact lock you purchase is certified accordingly.

Should I choose a 2½" or 3" lock?

The correct size depends on the door and position required for the handle and keyhole.

A 3" case provides a deeper backset, while a 2½" lock positions the door furniture closer to the door edge.

Can I replace an existing mortice lock?

Yes. Before ordering, check the case depth, backset, faceplate size and position of the spindle and keyhole.

Matching these dimensions as closely as possible can reduce the amount of alteration required to the door.

Can security locks be matched to my door handles?

Yes. The Atlantic locks within our range are available in multiple architectural finishes designed to coordinate with compatible door furniture.

Matching the lock faceplate to the handles, escutcheons and hinges can create a more consistent finished door.

Need Help Choosing a Security Lock?

The correct security lock will depend on your door location, required security level, lock type, case size and existing door preparation.

Roundtower Hardware supplies 5 lever security locks, mortice sashlocks and deadlocks in Ireland, including BS 3621 options for suitable entrance-door applications.

Browse our collection online or contact our team if you need help identifying the correct lock for your door.