How to Measure a Euro Cylinder

A euro cylinder is the barrel-shaped lock fitted into most uPVC and composite front doors in the UK. It is the component that your key turns. It has two sides — the external side, which faces out towards the street or communal hallway, and the internal side, which faces into your home. The two dimensions are always written as external x internal, separated by a slash, so a cylinder labelled 35/45 is 35 mm on the outside and 45 mm on the inside. The total length is 80 mm. That format is consistent across every reputable manufacturer, so once you know your two numbers you can shop or order a like-for-like replacement with confidence.

The danger comes when the external figure is too large. If the cylinder protrudes more than a couple of millimetres beyond the face of the door furniture — the outer escutcheon plate or handle surround — it offers a purchase point for a burglar using a snapping technique. They grip the exposed cylinder with a tool, apply rotational force, and the cylinder shears at a weak internal point, usually within seconds. The lock then opens without a key. This is not theoretical; it is the most frequently reported method of forced entry to uPVC doors in this part of south-east London. Measuring correctly, and then choosing an anti-snap TS007 3-star rated cylinder, removes that vulnerability entirely.

You need a steel ruler or a metal tape measure — a fabric tape can flex and give you a figure that is a millimetre or two out, which matters with cylinder sizing. Close and lock your door from the inside so the cylinder is in its natural seated position. First, locate the central fixing screw that runs through the door into the cylinder; this screw, when removed, allows the cylinder to slide out, but you do not need to remove it to measure. Place the end of your ruler at the outer face of the door furniture — not the door itself, but the escutcheon plate or handle surround — and measure to the centre of that fixing screw. This gives you your external dimension. Now measure from the same central fixing screw point to the inner face of the door furniture on the inside. That is your internal dimension. Write both numbers down: external first, then internal. If you get something like 40 and 50, your cylinder is a 40/50 and the total is 90 mm.

A quick check: if your external measurement is noticeably larger than your internal measurement, your cylinder may already be protruding too far. Hold a straight edge across the door face alongside the cylinder. If the cylinder nose sits proud of the door furniture by more than roughly 3 mm, it is at real risk of being snapped. That is the moment to call a professional and ask about a correctly sized anti-snap replacement — do not wait until something goes wrong. If you are unsure about your measurements or what they mean, our team is available around the clock. Call 020 3757 5599 and we can advise you over the phone before arranging a visit.

Once you have your measurement, you have three paths. If the cylinder is the correct size and in good condition, you may simply need a new one of the same dimensions with better security credentials — particularly an anti-snap, anti-pick, anti-drill cylinder rated to TS007 3-star. If the cylinder is the wrong size for the door furniture, it needs replacing with a correctly sized unit as part of a proper door lock replacement. And if the door itself has been damaged — either through attempted forced entry or simple wear to the multipoint locking mechanism — a broader repair or lock change Belvedere residents often need after a break-in attempt may be the right answer.

For tenants in a rented flat on Picardy Road or a house in Lessness Heath, it is worth checking with your letting agent before changing any lock yourself, as most tenancy agreements require landlord consent. For homeowners, the decision is straightforward: a correctly sized, high-security cylinder is a one-time job that costs far less in the long run than dealing with a burglary. Our team handles door lock replacement Belvedere wide, fitting cylinders that suit the exact door furniture already in place — no guesswork, no ill-fitting parts.

Measuring the cylinder is only part of the picture. uPVC doors rely on a multipoint locking mechanism — a strip of steel running up and down inside the door, with multiple hooks and bolts that engage when you lift the handle and turn the key. This mechanism can fail independently of the cylinder. Common signs include a handle that feels stiff or spongy, a key that turns but does not feel like it is engaging anything, a door that rattles in the frame even when locked, or a latch that drops but the hooks do not follow. These are all faults with the gearbox or the multipoint mechanism itself, not the cylinder. uPVC door lock repair Belvedere calls make up a significant portion of the work we attend, particularly on older doors where the mechanism has simply worn out after years of daily use.

The important distinction is that replacing only the cylinder when the mechanism is at fault will not solve the problem — and replacing only the mechanism when the cylinder is compromised leaves a security gap. A skilled locksmith will assess both during any visit. If you have been locked out Belvedere-side because a handle has dropped at an awkward moment and the door will not open from either side, that is almost always a mechanism failure rather than a cylinder issue. Do not attempt to force the door; instead call 020 3757 5599 and we will send someone straight away. We are usually with you in about 30 minutes, and we confirm an exact up-front price before any work begins — the final quote depends on factors including the lock type, parts required, time of day, and travel distance.

If you are locked out of your home in Belvedere right now, the first sensible steps are to check whether a window has been left on the latch, whether a trusted neighbour holds a spare key, or whether there is a back door you can access safely. If none of those options apply, do not attempt to force a lock or use a card to slip a latch — beyond the safety risk, you may cause additional damage that increases the cost of the repair. As a 24 hour locksmith Belvedere residents rely on around the clock, we handle genuine lockouts as a matter of priority. Ownership verification is a normal part of our process — we may ask for a form of identification or proof of address before beginning work, which is standard practice and something any responsible professional should do.

If your door shows signs of a snapping attempt — a cylinder that is partly turned, a door that has been opened without a key, or visible tool marks around the lock — treat it as an active security concern. Do not simply push the cylinder back in and carry on. The door is no longer secure, and you need a professional assessment, potentially including a full lock change and an inspection of the door frame and furniture. Our emergency locksmith Belvedere service covers exactly these situations, day or night, including evenings, weekends, and bank holidays. We are a mobile team serving Erith, Belvedere, Abbey Wood, Slade Green, and surrounding areas — if you are in the DA8 or DA18 postcode district, we can reach you.

These four terms are often used interchangeably but they mean different things in practice, and knowing the difference helps you describe your situation clearly when you call. Replacement means fitting a new cylinder or mechanism in place of an existing one of the same type — the door furniture and door itself stay as they are. Installation refers to fitting a lock to a door that did not previously have one, or fitting an entirely new type of lock system to a door. Change the lock or change the cylinder means swapping out the existing security component, usually for a higher-specification one or because a previous key holder still has access. Repair means fixing a fault with an existing mechanism — a stiff handle, a misaligned latch, a broken gearbox — without necessarily replacing the whole unit.

Understanding which you need helps a locksmith give you an accurate quote over the phone and arrive with the right parts. When you call 020 3757 5599, our team will ask you a few straightforward questions — what type of door you have, what you can see happening (or not happening) with the lock, and roughly when the problem started. From there we can tell you what is likely needed and confirm a fixed price before we come out. There are no surprises on arrival.