How to Measure a Euro Cylinder

A euro cylinder is the barrel-shaped locking mechanism that sits inside the lock case of most modern uPVC, composite, and aluminium doors. You will recognise it by its distinctive figure-of-eight cross-section — two circular sections joined together, with a keyhole on one or both ends and, in some versions, a thumb-turn on the inside. The cylinder itself does not contain the handle, bolt, or multipoint mechanism; it simply operates them when you turn the key. Because it is a standard shape, cylinders from different manufacturers are largely interchangeable, which is both convenient and, if the wrong one is fitted, a genuine security risk.

On a typical Walthamstow terrace with a uPVC front door — common in the streets around Hoe Street, Orford Road, and Forest Road — the euro cylinder will be held in place by a single screw through the door edge into the lock case. That screw is the only thing stopping a correctly sized anti-snap cylinder from being removed by force. If the cylinder sticks out beyond the door handle or escutcheon plate, a thief can grip the exposed section with grips or pliers and snap it at a designed weak point, releasing the door in seconds without any noise, without picking the lock, and without breaking glass.

You will need a tape measure — a standard retractable one is fine — and a notepad. Start by opening your door so you can reach both sides easily. The measurement you are looking for is the total length of the cylinder and how that length is split between the outside (the keyhole side, exposed to the street) and the inside (the thumb-turn or second keyhole side, inside your home). These two figures are always written as a pair: for example, 35/45 mm, meaning 35 mm on the outside and 45 mm on the inside, giving a total of 80 mm.

To take the measurement, locate the fixing screw on the door edge — it usually sits in the middle of the door edge, roughly at the same height as the lock case. That screw marks the centre of the cylinder. Measure from the centre of that screw to the face of the door on the outside; write that figure down. Then measure from the centre of the screw to the face of the door on the inside. Add the two together for the total. Double-check by measuring the cylinder itself if it is already removed: lay it flat, measure from end to end, then find the centre cam (the small metal lug that rotates when you turn the key) and measure each side independently. A difference of even 5 mm between what you measure and what you buy will mean either the cam does not align with the lock case, or the cylinder protrudes — so accuracy matters.

Lock snapping is not a niche concern — it has been a recognised method of burglary across London for well over a decade, and homes with standard, oversized, or poorly fitted cylinders remain at risk. The technique exploits the fact that standard euro cylinders have a deliberate stress point built in; manufacturers include it so that if someone applies excessive rotational force to the key, the cylinder breaks before the lock case is damaged. Burglars learned to use that feature by gripping the protruding outside section and applying sideways force rather than rotational force, snapping the front of the cylinder off cleanly and accessing the cam directly.

The fix is straightforward: fit a cylinder that is the correct size so nothing protrudes beyond the external door furniture, and choose one that carries a TS007 3-star rating or at minimum an anti-snap designation. These cylinders have hardened steel inserts and reinforced snap lines that make the snapping technique impractical. Many home insurers — particularly for properties in London postcodes — now specifically ask whether your cylinder meets this standard. Getting the size right is therefore not just about whether the key turns smoothly; it is the first step in making the upgrade meaningful. If you are unsure whether your current cylinder is correctly sized or meets the right security grade, our experienced locksmiths can assess it quickly. Call 020 3757 6115 — we cover Walthamstow and the wider east London area, 24 hours a day.

Once you have your measurements, write them in the format outside/inside — so 35 mm on the street side and 45 mm on the home side becomes 35/45. When shopping for a replacement, match this exactly. If your door has a handle in the centre of the door furniture rather than near the top or bottom, the inside measurement will almost always be longer than the outside measurement because the thumb-turn needs room to operate comfortably. For doors where the handle is offset, the figures may be equal or the outside may be longer — measure carefully rather than assuming.

On the security grading side, look for TS007 3-star cylinders, or cylinders that combine a 1-star rating with a 2-star door handle to reach the same overall standard. The Sold Secure Diamond rating is another reliable marker. Anti-pick, anti-drill, and anti-bump features are worth having alongside anti-snap protection, since a skilled burglar will try whichever technique is fastest. Landlords and letting agents in Walthamstow should note that upgrading to a 3-star cylinder when changing a lock is a simple step that strengthens a property between tenancies and can satisfy insurance requirements without a full door lock replacement London-wide. If you would rather have a qualified locksmith handle the selection and fitting — particularly after a break-in attempt, a snapped cylinder, or simply because you want the job done correctly the first time — our team carries a range of rated cylinders and can advise on the right grade for your specific door.

Knowing how to measure a euro cylinder is genuinely useful, but there are situations where measuring is only the starting point — or where the right course of action is to call a professional rather than attempt a DIY change. If your cylinder has already been snapped, partially snapped, or tampered with, the lock case underneath may also be damaged, and fitting a new cylinder without inspecting the case can leave the door insecure even after the work is done. Similarly, if a key has broken inside the cylinder or the cylinder spins freely without operating the lock, the internal mechanism may need attention beyond a straight swap.

A door lock replacement London homes or flats might need following a burglary, an eviction dispute, or a change of tenancy is a job where getting the right parts and correct fitting matters enormously — a poorly fitted cylinder on a composite door can leave gaps that compromise the weather seal as well as the security. Our team carries out upvc door lock repair London residents rely on after damage or wear, and we handle full lock change London work across E17, E10, E11, and surrounding postcodes. If you are locked out London and need help right now, do not attempt to force entry or try to pick a door knob lock yourself — check for a spare key with a trusted neighbour or family member first, then call us. We will send a locksmith straight away and are usually with you in about 30 minutes. For non-emergencies, the same number reaches our team day and night: 020 3757 6115.

Walthamstow Locksmith is a mobile, 24 hour locksmith London service covering Walthamstow and the surrounding east London area. Whether you need a cylinder measured and swapped, a full multipoint lock mechanism replaced, or emergency locksmith London assistance after a break-in, we provide an exact quote before any work begins — no surprises on the final bill. The price we confirm on the phone is the price you pay, and it reflects the type of lock involved, the time of day (evenings, weekends, and bank holidays are factored in clearly), travel to your address, and any parts needed.

Our services include: euro cylinder replacement, anti-snap cylinder upgrades, TS007 3-star cylinder fitting, uPVC door lock repair, composite door lock repair, multipoint lock mechanism replacement, Yale nightlatch fitting and replacement, 5-lever mortice deadlock fitting, BS3621 compliant lock upgrades, wooden door lock changes, emergency door opening after lockout, burglary damage repair, broken key extraction, door alignment and adjustment, door furniture replacement, letterbox replacement, thumb-turn cylinder fitting, double-cylinder fitting for glazed doors, communal entrance lock replacement, lock change for landlords between tenancies, lock change on instruction from a letting agent, security surveys and cylinder grading advice, anti-drill and anti-pick cylinder upgrades, door hinge bolt fitting, and door reinforcement advice. All work is carried out by trained, experienced, and fully insured locksmiths.

There is no shortage of people offering locksmith services across London, and not all of them will give you an honest price, the right advice on security ratings, or a properly fitted cylinder. When you search for help, look for a locksmith who will give you a clear quote before arriving, explain exactly what parts they intend to fit and why, and carry the relevant security-rated stock rather than fitting whatever is cheapest or easiest to source. Ask whether the cylinder they plan to fit is anti-snap and what star rating it carries. A skilled, experienced locksmith will welcome those questions.

At Walthamstow Locksmith, we work exclusively in the local area — we know the door types common in E17, the multipoint lock brands fitted to newer builds around Blackhorse Road, and the older timber doors in the Victorian terraces near St James Street station. That local familiarity means we arrive prepared. We are not a matching service or a directory that passes your details to whoever is available; we are a local team, fully insured, and reachable at 020 3757 6115 any time of the day or night.