How to Measure a Euro Cylinder

A euro cylinder is the oval-shaped locking mechanism that sits inside the lock housing on most modern uPVC and composite front and back doors in the UK. It is the part your key actually enters, and it is held in place by a single central bolt called the retaining screw. If you have a uPVC door — extremely common in Beckenham's mix of 1930s semis that have had their original timber doors replaced, and in the blocks of flats around Bromley Road — the chances are high that you have a euro cylinder. Traditional timber front doors are more likely to have a 5-lever mortice deadlock and a Yale-type nightlatch, but even many of those have euro cylinders fitted to secondary locks.

Euro cylinders come in a huge range of sizes, and fitting the wrong size is one of the most common and costly mistakes a homeowner can make. A cylinder that is even a few millimetres too long on the outside of the door becomes a lever point for a would-be intruder using a technique called cylinder snapping, in which the exposed portion is broken off in seconds with a simple tool. That is why measuring correctly — and understanding the result — matters far more than most people realise.

You need a tape measure or a ruler. Start by opening your door so you can examine the cylinder from the inside edge. The cylinder runs horizontally through the door, and the measurement is always taken in two halves: the external (outside) measurement and the internal (inside) measurement, with the two numbers written as external x internal — for example, 35/45 or 40/50. Here is how to take each measurement accurately. First, locate the central spindle — this is the small cam or bar in the very middle of the cylinder that connects to the door mechanism. Measure from the outside face of the door to the centre of that spindle. Write that number down — this is your external figure. Then measure from the inside face of the door to the centre of the spindle. That is your internal figure. Add the two together and you have the total cylinder length. A very common size in UK residential doors is 35mm outside and 45mm inside, written as 35/45 and totalling 80mm. If you are unsure where the exact centre of the spindle sits, measure to the retaining screw hole instead — it passes through the spindle and gives you a reliable reference point.

A few important notes: always measure with the door in its frame and from the face of the door, not from the edge of any furniture or handle plate, because the handle plate does not affect the measurement. If your door has a handle plate that sits proud of the door surface, measure to the door face itself. When in doubt, measure twice. If you find the external measurement is notably larger than the internal one — say 50mm outside versus 35mm inside — that overhang is exactly what makes the cylinder vulnerable to snapping. The goal when choosing a replacement is to have the cylinder sitting flush with the outer face of the door, or as close to flush as your handle allows, with no more than a couple of millimetres of protrusion.

Lock snapping has been a well-documented problem in the UK for well over a decade. The technique exploits the fact that standard euro cylinders have a weak point — a narrow section between the two halves of the barrel. When the external portion protrudes beyond the door furniture, a burglar can grip or lever that exposed section and snap the cylinder at that weak point in a matter of seconds, often silently and without leaving obvious damage. It is one of the primary methods used in burglaries affecting uPVC and composite doors across Greater London and the South East, including areas like Beckenham, Penge, and West Wickham.

The answer is a TS007 3-star rated anti-snap cylinder, or a combination of a 1-star cylinder with 1-star door furniture and 1-star handle, together totalling 3 stars. These cylinders are engineered to snap in a sacrificial zone that leaves the internal locking mechanism intact and the door secure. Many home insurers now specifically ask whether your door locks meet British Standard TS007 3-star or BS3621, and fitting a non-compliant cylinder could affect a claim. If you have established that your current cylinder protrudes significantly, that is a conversation worth having with a professional. For door lock replacement Beckenham residents can trust, our team carries a range of correctly sized, anti-snap cylinders and can confirm the right size on the spot before fitting anything.

The most frequent mistake people make when looking to change a door lock or replace a euro cylinder is buying a standard pack from a DIY shop based on a rough guess rather than a measured figure. Because cylinders come in increments of 5mm, even a 5mm error in your measurement can mean the difference between a flush, secure fit and a dangerously protruding one. Another common error is confusing the total length with the split measurement — ordering an 80mm cylinder expecting 40/40, only to find the door is actually 35/45 and the cylinder sits 5mm too proud on the outside. Always write both individual measurements down before you buy or order anything. If you are dealing with a uPVC door lock repair Beckenham — perhaps a cylinder that has stiffened up or a mechanism that has started to feel loose — the cylinder measurement is the starting point for every diagnosis.

If you are locked out or the door has been damaged, do not attempt to force the cylinder or try improvised methods to bypass the lock. The risks of damaging the door frame, the multipoint lock mechanism, or injuring yourself are real, and a damaged frame can be significantly more expensive to put right than a straightforward lock replacement. The right step is to call a professional locksmith straight away. If you are facing an urgent situation right now — a lock that will not turn, a door that will not open, or a cylinder that has already snapped — call us on 020 3757 5562. We operate as a 24 hour locksmith Beckenham and the surrounding area, and we will send a locksmith straight away, usually with you in around 30 minutes.

Once you have your two measurements written down — say 35mm outside and 45mm inside — you are looking for a cylinder marked 35/45 in the correct security grade. For most Beckenham homes, we recommend a minimum of a TS007 3-star anti-snap cylinder, particularly on front doors. If your door has been showing signs of wear — the key is stiff, the cylinder feels loose in the housing, or the cam inside is not quite catching the mechanism cleanly — it is worth replacing the entire cylinder rather than simply lubricating the existing one, especially if that cylinder is more than a few years old or is a standard, non-anti-snap model.

When one of our locksmiths carries out a lock change Beckenham, the process is straightforward. The retaining screw is removed, the old cylinder is drawn out, the new one is offered up and checked for fit before final tightening, and the door is tested through several full lock and unlock cycles before we pack up. We always confirm the exact price before any work begins, and that price reflects factors including the cylinder type, the complexity of the door mechanism, the time of day — evenings, weekends and bank holidays can affect the call-out charge — and travel to your address. There are never any hidden costs added afterwards. If you have a uPVC door, composite door, or a timber door with a euro cylinder, the measurement steps above apply equally, and our team can advise on the best cylinder for your specific door and frame during the visit. As your local locksmith Beckenham, we also cover Shortlands, Clock House, Eden Park, Elmers End, Penge, and surrounding postcodes. For anything from a straightforward cylinder change to an emergency lockout, call 020 3757 5562 — we answer 24/7.

We are a fully insured, mobile locksmith service operating across the Beckenham area and nearby neighbourhoods. Here is a full list of the specific services our skilled team provides: euro cylinder measurement and replacement; anti-snap TS007 3-star cylinder upgrades; uPVC door lock repair Beckenham; multipoint lock mechanism repair; multipoint lock mechanism replacement; uPVC door realignment and adjustment; composite door lock repair; composite door cylinder replacement; wooden door 5-lever mortice deadlock supply and fitting; Yale nightlatch replacement; Yale nightlatch upgrade; door lock replacement Beckenham across all door types; emergency locksmith Beckenham response for lockouts; non-destructive entry where possible; lock change Beckenham after a break-in; lock change following a lost key; lock change after a tenancy change; communal entrance lock repair for blocks of flats; flat front door lock replacement; door frame repair following forced entry; uPVC door handle and mechanism replacement; door furniture upgrade to meet insurer requirements; BS3621 mortice deadlock supply and fitting; lock health check and security audit for your front and back doors; and 24 hour locksmith Beckenham cover on evenings, weekends and bank holidays.