Euro Cylinder Locks Explained: Types, Sizes and Security

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 alike to develop quality ironmongery that stands the test of time. Read my full bio.

A euro cylinder lock is the replaceable, key-operated barrel used in a compatible door lock. Turning the key, or an internal thumbturn, rotates a cam that operates the locking mechanism. The cylinder is a separate component from the lock case or multipoint strip inside the door.

Choosing a replacement means checking more than its total length. You need the correct internal and external measurements, the right operating arrangement and a security specification suitable for the door. This guide explains the differences and introduces our euro cylinder lock collection.

What is a euro cylinder lock?

A euro cylinder has a recognisable profile: a rounded upper section above a narrower lower section. The key operates the cylinder, while its central cam acts on the mechanism within the lock case. This arrangement often allows the keys to be changed by replacing the cylinder rather than the complete lock.

Euro cylinders can be used in compatible locks on timber, uPVC and composite doors. The door material alone does not establish compatibility. Check the lock manufacturer's requirements for the cylinder, cam and operating function.

Three terms are worth separating:

• Euro cylinder: the key-operated component and its profile.
• Euro sash lock: a lock case with a handle-operated latch and a deadbolt operated through the cylinder.
• Euro deadlock: a lock case with a deadbolt but no handle-operated latch.

A compatible multipoint lock can also use a euro cylinder. Changing that cylinder does not replace the gearbox, hooks or bolts elsewhere in the system.

Antique Brass Euro 15 Pin Cylinder - Key to Turn

Matt Black Euro 15 Pin Cylinder - Key to Turn

Key-to-key, thumbturn and single cylinders

Key-to-key: keyed operation on both sides

A double cylinder, also called key-to-key, requires a key to operate it from either side of the door. Consider how occupants will leave when the door is locked: requiring an internal key is not appropriate for every situation.

Do not assume the outside key will work while another key is left inside. That depends on whether the exact cylinder has a suitable emergency or double-function arrangement.

Key-to-turn: a key outside and a thumbturn inside

A key-to-turn cylinder is keyed externally and has a thumbturn internally. It allows the cylinder to be operated from inside without finding a key.

A euro thumbturn cylinder is not the same as a separate bathroom turn-and-release fitting. It remains part of a cylinder-operated lock. For escape doors, check the requirements of the complete locking arrangement rather than assuming any thumbturn makes the door compliant.

Single cylinder: keyed operation from one side

A single or half cylinder has one key-operated side. It is intended for compatible applications where cylinder operation is needed from one side only, such as certain cupboard locks. It does not provide an internal thumbturn.

Polished Chrome Euro 15 Pin Double Cylinder - Key To Key

Satin Brass Euro 15 Pin Double Cylinder - Key To Key

Keyed alike and key to differ

Key to differ means the cylinders are supplied with different key combinations. Keyed alike means a specified group of cylinders is arranged to work with the same key.

Keyed alike can reduce the number of keys you carry, but losing that key affects every cylinder in the set. Confirm the required group when ordering; simply buying several cylinders of the same model does not make them keyed alike.

A master-key system is different: individual keys operate their assigned cylinders, while a master key operates a wider group. Do not assume ordinary keyed-alike products provide that arrangement.

Euro cylinder sizes explained

The overall length is only part of the measurement. The position of the lock within the door, together with the handles or escutcheons on each face, determines how much cylinder is needed on either side.

When using centre-based measurements, record:

1. The external side: from the centre of the cylinder retaining-screw hole to the external end of the cylinder body.
2. The internal side: from the same centre to the internal end of the cylinder body.
3. The overall body length: the two centre-based measurements added together, excluding the projecting thumbturn or key.

For example, a centre-measured 35/35 cylinder is 70 mm overall. A 30/40 cylinder is also 70 mm overall, but the offset is different. They are not automatically interchangeable. Label your measurements “inside” and “outside”, especially when ordering a thumbturn cylinder.

Antique Brass Euro 5 Pin Double Cylinder - Key To Key

Satin Chrome Euro 5 Pin Double Cylinder - Key To Key

If the existing cylinder projects too far, do not simply copy its size. Check the required length against the outer faces of the fitted handles or escutcheons and the manufacturer's permitted projection. Door thickness alone is not enough, and changing the surrounding hardware can change the required length.

For the detailed measuring and fitting sequence, see how to measure and fit a euro cylinder lock.

5-pin and 15-pin cylinders

The five-pin cylinders in our range are listed for basic internal-door security. The fifteen-pin options are offered for external-door applications, subject to the specification required for the particular door.

The fifteen-pin arrangement described here uses six active pins and nine passive pins, as specified for these AGB cylinders. It should not be interpreted as fifteen identical active pins, or as a security rating based on the number alone.

Use the following table to identify the operating option, then check the dimensions and specifications on the individual product page.

These are cylinder body lengths, not recommended door thicknesses. Check the internal and external dimensions, finish and required certification before ordering.

Antique Brass Matt Black Euro 5 Pin Single Cylinder

Matt Black Euro 5 Pin Single Cylinder

Security features and ratings

Security descriptions refer to different things. Anti-drill protection addresses drilling, anti-pick and anti-bump features address forms of manipulation, and anti-snap protection addresses cylinder-snapping attacks. An anti-pull feature does not, by itself, establish an anti-snap rating.

EN 1303

EN 1303 classifies several aspects of cylinder performance, including key-related security and attack resistance. A reference to the standard alone does not tell you every grade achieved. Ask for the classification and supporting certificate where a project requires a particular performance level.

TS 007 and Sold Secure

For enhanced cylinder protection, the Door & Hardware Federation describes two TS 007 arrangements: a certified three-star cylinder, or a certified one-star cylinder used with certified two-star protective hardware. An ordinary decorative handle or escutcheon is not a substitute for rated protective hardware.

Sold Secure SS312 Diamond is a separate cylinder approval to look for where specified. Check the exact model in the Sold Secure cylinder directory rather than relying on a general description such as “high security”. The DHF guidance on cylinder security explains the different protection arrangements.

Euro profile and British Standards are not alternatives

“Euro” describes the cylinder profile. “British Standard” refers to a particular standard and, where applicable, a certified product or locking assembly. A euro-profile arrangement can form part of a certified lock. Do not assume that a cylinder's EN 1303 classification proves the complete lock meets BS 3621.

Choosing a cylinder for your door

• Check the application. An internal cupboard and an entrance door can have different security and access requirements. Do not choose an entrance-door cylinder by finish or pin count alone.
• Match the mechanism. Confirm the profile, cam and any clutch or free-running function required by the lock manufacturer. Matching the length does not establish full compatibility.
• Plan internal exit. Decide whether a key or thumbturn is appropriate. For an escape route, use the specified locking arrangement and seek advice if unsure.
• Check fire-door evidence. A cylinder's fire-test claim is not permission to fit it to every fire door. Follow the door manufacturer's approved hardware requirements and use a competent installer where needed.
• Check your insurance wording. Requirements vary. Confirm any named standard or locking arrangement rather than relying on the phrase “insurance approved”.
• Choose the finish last. Match the visible cylinder finish to the surrounding hardware after its size, operation and specification are settled.

Replacing the cylinder or the whole lock

If the lock mechanism is serviceable and the aim is to change the keys, replacing a compatible cylinder may be enough. However, a stiff door, dropping handle or damaged multipoint gearbox is not necessarily a cylinder fault.

Follow the instructions for the exact lock. On a conventional removable euro cylinder, the cam normally needs aligning before the cylinder will slide out; removing the retaining screw alone may not release it. Never force a cylinder that will not move.

Use our measuring and fitting guide for the full sequence. If the door is locked shut, the mechanism is damaged or the cylinder cannot be removed normally, ask a locksmith to assess it.

Polished Chrome Round Brass Escutcheon Euro

Satin Brass Round Brass Escutcheon Euro

Conclusion

Start with the door and its lock, then choose the cylinder's operation, internal and external dimensions, and required security rating. Keyed-alike options and matching finishes can then be considered without losing sight of compatibility.

Browse our euro cylinder lock collection, and use the individual product drawings before ordering. If you are unsure, send us the measurements and details of the existing lock so we can help check the available options.

Related Blog Posts

• How to Choose Handles for an Internal Door
• How to Measure and Fit a Euro Cylinder Lock
• What Is a Sash Lock?
• Multipoint Door Handles and Locks Explained

Frequently Asked Questions

Are all euro cylinder locks the same size?

No. Euro cylinders share a recognisable profile, but their overall lengths, internal and external measurements, operating arrangements and security specifications vary. Check the exact product drawing and the requirements of the existing lock before ordering.

What does 35/35 mean on a euro cylinder?

When both dimensions are measured from the fixing-screw centre, 35/35 means 35 mm on each side and 70 mm overall. Some drawings label the central section separately, so always check where each dimension starts and ends.

Is a 15-pin cylinder automatically more secure than a 5-pin cylinder?

Pin count alone does not establish a cylinder's security rating. The 15-pin arrangement described here has six active pins and nine passive pins. Compare the exact cylinder's tested protection and certification, as well as its fit and suitability for the door.

What is the difference between key-to-key and key-to-turn?

A key-to-key cylinder requires a key on both sides. A key-to-turn cylinder uses a key outside and a thumbturn inside. Choose the arrangement that meets the door's access and escape requirements; neither description alone establishes its security rating.

Can several euro cylinders use the same key?

Yes, cylinders supplied as a compatible keyed-alike set can use the same key. Ordering several ordinary key-to-differ cylinders does not achieve this. Confirm the required set and whether further matching cylinders can be supplied before ordering.

Can I replace a euro cylinder without replacing the whole lock?

Often, yes. A compatible euro cylinder can usually be replaced while retaining a serviceable lock case or multipoint mechanism. A new cylinder will not repair a damaged gearbox, misaligned door or other fault elsewhere in the locking system.

Are euro cylinders British Standard locks?

Euro describes the cylinder profile, not a security certification. A euro-profile locking arrangement can form part of a British Standard-certified lock, but the certificate must cover the relevant product or assembly. Do not treat pin count or a reference to EN 1303 as proof of BS 3621 or TS 007 certification.