How to Measure a Euro Cylinder

A euro cylinder is the oval or D-shaped barrel that sits inside the lock housing on most modern uPVC and composite front and back doors. You can spot it immediately — it is the part the key goes into, and it has a small cam or tailpiece at its centre that rotates to throw or retract the bolt when the key turns. Euro cylinders are found across millions of homes in Kentish Town, Camden and throughout London, and they are almost always secured by a single grub screw on the edge of the door. That is both their convenience and, unless you choose the right type, their vulnerability.

The measurement matters for two reasons. First, a cylinder that is the wrong length simply will not fit — if the fixing screw hole does not align with the cam, the door will not lock at all. Second, and more critically from a security perspective, a cylinder that protrudes more than roughly 3 mm beyond the outer face of the door is exposed enough for an attacker to grip with pliers, apply rotational force, and snap the cylinder in half in a matter of seconds. Once snapped, the door can be opened without a key in under a minute. This snapping technique has become the dominant method of forced entry on uPVC and composite doors across London, which is why getting the external measurement right — and choosing an anti-snap, TS007 3-star rated cylinder — is not optional if you care about your home's security.

You need a metal tape measure or a steel rule — a soft fabric tape can flex and give a misleading reading. Open your door so you can see the cylinder from both faces, and locate the centre point: this is the fixing screw or the small hole where the grub screw sits, usually on the door edge. This centre point divides the cylinder into two halves — the external measurement (from the outer face of the door furniture or the cylinder's outer end to the centre) and the internal measurement (from the centre to the inner end, usually the thumb-turn side on a double-cylinder or key-turn on a single). Write both numbers down in millimetres. A common size on a standard 44 mm door slab is 35 mm on the inside and 35 mm on the outside, written as 35/35 or 70 mm total, but doors vary — particularly older timber doors in the Victorian and Edwardian terraces you find along Kentish Town Road and the surrounding streets, where door thicknesses can differ noticeably from one property to the next.

Once you have your two measurements, add them together to confirm the total length. When you specify a replacement, always give both individual figures — not just the total — because the position of the cam relative to the door face is what determines whether the cylinder sits flush or protrudes. If your existing cylinder protrudes and you are using this as an opportunity to improve security, you can order a cylinder that is 5 mm shorter on the external side so it sits at or just below the face of the escutcheon. Many professional locksmiths — including our team across the Kentish Town area — will also check whether the existing door furniture (the outer handle plate or escutcheon) can accommodate the new cylinder before confirming the right size for you. If you are unsure at any point, calling 020 7871 7825 means you can describe what you see and we can advise you before you order anything.

Lock snapping is not a theoretical risk — it is the method that accounts for a large proportion of burglaries on uPVC and composite doors across London. The attack works because a standard euro cylinder is designed to break at a sacrificial shear line when enough rotational force is applied. That is a manufacturing feature, not a flaw — it prevents the internal mechanism being destroyed — but it becomes a vulnerability the moment the outer end of the cylinder is exposed enough to grip. If the cylinder protrudes more than 3 mm beyond the door furniture, a burglar can apply force with nothing more sophisticated than a cheap pair of adjustable pliers and have the outer section off in seconds. After that, a flat-head screwdriver engages the remaining cam directly and the door opens.

The defence is straightforward: a correctly sized cylinder that sits flush or slightly recessed, combined with an anti-snap cylinder that includes an additional internal sacrificial break point positioned so that even if the outer section is snapped off, the cam and locking mechanism remain protected. Look for cylinders rated to TS007 3-star or carrying the Sold Secure Diamond rating. When we carry out a door lock replacement London-wide, we always fit anti-snap cylinders as standard because there is no sensible reason to fit anything less. If you are a tenant, your landlord or letting agent has an obligation to maintain the security of your front door, and upgrading to an anti-snap cylinder is a reasonable improvement that most managing agents will approve readily.

Once you have your measurements, the second decision is the security grade. At the entry level you have standard, non-rated cylinders — these are the ones to avoid. Above them sit cylinders meeting BS EN 1303 at Grade 6, which offers basic pick and drill resistance. The standard genuinely worth specifying for a London home is the TS007 3-star rating, which covers anti-snap, anti-pick, anti-drill and anti-bump performance in a single independently tested product. Some insurers in the UK now specifically ask for TS007 3-star cylinders on front doors, so it is worth checking your home insurance policy documents before you buy. A related standard is Sold Secure Diamond, which covers much of the same ground. Neither rating costs dramatically more than a basic cylinder, and either one is a meaningful upgrade if your existing lock is a standard chrome or brass barrel that came fitted when the door was installed.

[10] It is also worth thinking about the keyway. If everyone in your household has the same key profile and you are simply replacing a worn or damaged cylinder, stay with the same profile so existing keys continue to work. If, however, you have recently moved into a property, have lost a key, or have had a tenancy change, this is the right moment to think about how to change a lock properly — meaning a full cylinder replacement rather than any attempt to modify the existing barrel, which on a euro cylinder is not straightforward and rarely recommended. Our experienced locksmiths carry a range of anti-snap cylinders in common sizes and can usually complete a door lock replacement on the same visit. If you need uPVC door lock repair London or a full cylinder swap on a composite door, call 020 7871 7825 and we will confirm an exact up-front price before we come out — no surprises on the invoice.

Measuring and ordering a cylinder yourself is entirely achievable, and for a planned upgrade on a door you can still lock and use, there is no reason not to do it. However, there are situations where calling a 24 hour locksmith London is the right call rather than a last resort. If you are locked out London and cannot access your property, attempting to remove the cylinder yourself from the outside without the key is not safe or practical — it is precisely the kind of manipulation that should be carried out by a skilled professional who can verify ownership and use the right techniques without damaging the door. Similarly, if your cylinder has already been attacked, partially snapped, or is so worn that the key no longer turns reliably, trying to unscrew and replace it yourself risks leaving the door inoperable mid-job. If the grub screw has seized — common on older uPVC doors — forcing it can strip the thread in the door edge, which then requires a more involved repair.

There is also the question of time of day. A lock that starts playing up at 11pm on a Sunday or on a bank holiday is still a security issue that needs sorting before you go to bed. As a 24 hour locksmith London, we respond to calls at all hours — evenings, weekends, bank holidays — and we send a locksmith straight away, aiming to be with you in around 30 minutes depending on where you are in the Kentish Town area and surrounding postcodes. As a lock change London service operating across the city, we cover everything from straightforward cylinder swaps to more complex uPVC multipoint lock repairs, and as an emergency locksmith London, we are equally at home dealing with a lockout at 2am as a planned security upgrade at 10 in the morning. The factors that influence the final price include the type of cylinder or lock required, the time of day, travel distance and any parts needed — all of which we confirm clearly over the phone before we set off.

Our mobile team handles a wide range of residential lock and door security work throughout Kentish Town and the wider London area. Here is what we cover: euro cylinder measurement and replacement; anti-snap cylinder upgrades; TS007 3-star cylinder fitting; uPVC multipoint lock repair and replacement; uPVC door lock repair London; composite door lock servicing; Yale nightlatch replacement; 5-lever mortice deadlock fitting; BS3621 mortice deadlock installation; timber door lock changes; communal entrance door lock repair; flat front door lock replacement; door lock replacement London (all door types); emergency lockout response; non-destructive entry for residential lockouts; lock change London after a house move; lock change following a lost or stolen key; lock change following a tenancy change; door alignment and adjustment (when a misaligned door causes a lock to stick or fail to engage); escutcheon and door furniture fitting; anti-drill and anti-bump lock upgrades; door reinforcement bar fitting; letter box restrictor fitting; snapped cylinder removal and replacement; and post-break-in emergency boarding and lock replacement. If your situation is not on this list, call 020 7871 7825 and describe what you need — we will tell you straightforwardly whether we can help and confirm a price before anyone comes out.