How to Measure a Euro Cylinder

A euro cylinder is the oval-shaped barrel that sits inside your door lock and contains the keyway. Turn the key and a cam at the back of the cylinder rotates to operate the multipoint locking mechanism that runs up and down the edge of your door. Because the cylinder is a removable, standardised component, changing a lock or upgrading your security on a uPVC or composite door usually means swapping the cylinder rather than replacing the whole lock case — a job a skilled locksmith can complete in a matter of minutes.

The size matters for two reasons. First, a cylinder that is too short will not reach the fixing screw hole at the centre of the lock and simply will not work. Second — and this is the security issue most homeowners do not know about — a cylinder that protrudes beyond the outer face of your door handle or rose is vulnerable to snapping. A burglar can grip the exposed section with pliers or a mole wrench, snap the cylinder in two, and use a screwdriver to operate the cam directly. The whole process takes under a minute and makes no noise. This is not a theoretical risk; it is one of the most common break-in methods recorded by police across Cambridgeshire and the rest of the UK.

You need a tape measure or a steel rule, a screwdriver, and something to write on. Start by opening your door fully so you have clear access to both faces. Look at the cylinder — it passes through the door from the outside keyhole to the inside thumb-turn or keyhole. The single fixing screw sits in the edge of the door and passes through the centre of the cylinder; that centre point is your reference. Measure from the centre of the fixing screw to the outside face of the door (the face that faces the street). Write that number down — this is your external measurement. Then measure from the centre of the fixing screw to the inside face of the door. Write that down too — this is your internal measurement. A cylinder is always quoted as external measurement first, then internal: for example, 35/45 means 35 mm on the outside and 45 mm on the inside.

Now check for protrusion. Close the door and look at the outer keyhole. Is the cylinder flush with the face of the handle, rose, or escutcheon plate, or does it stick out beyond it? Even 2–3 mm of protrusion is enough for a snap attack to succeed. If the cylinder protrudes, you need a shorter external measurement or, ideally, an anti-snap cylinder with a sacrificial break point built in. The British Standard TS007 3-star rating is the benchmark to look for — these cylinders are designed to snap at a sacrificial section before the cam is ever reached, making the attack useless. Many home insurance policies in the UK also favour or require TS007-rated cylinders, so fitting one can be a condition of your cover as well as a genuine security upgrade. If you are unsure whether your current cylinder meets this standard, our team at Chesterton Locksmith can assess it and advise you honestly — call 01223 912859 and we will talk you through the options before anyone travels out.

The most frequent mistake is measuring the total length of the cylinder rather than measuring each side from the centre. If you measure end to end and divide by two, you will almost always get the wrong split — most cylinders are not symmetrical, because the internal side is typically longer to accommodate the thumb-turn mechanism. Always measure each side independently from the centre point of the fixing screw hole.

The second mistake is forgetting to account for the door furniture. Some handles and escutcheons are recessed into the door face, which effectively shortens the exposed portion of the cylinder without changing the cylinder itself. If your handle is recessed by 5 mm, a cylinder that would otherwise protrude by 3 mm is actually sitting 2 mm proud — still a risk, but a smaller one. Conversely, if you fit a new handle that sits further out from the door face, a cylinder that was previously flush may suddenly protrude. Always check protrusion after fitting any new door furniture, not just after changing the cylinder. If you are arranging a door lock replacement Cambridge or fitting new handles across a property, our team checks this as a matter of course.

Cylinder snapping became widespread in the UK roughly fifteen years ago as the quality of uPVC and composite doors improved — ironically, the stronger the door, the more a burglar needs to attack the cylinder rather than the frame. Cambridge is not exempt from this. Streets near the city centre, the Romsey area, and routes close to the A14 corridor have all seen opportunistic break-ins where the method of entry was cylinder snapping rather than glass breaking or door kicking. The attack leaves almost no trace on the door frame, which can complicate insurance claims if you cannot show the method of entry.

The practical takeaway is straightforward: if your cylinder protrudes, treat it as an urgent task rather than a someday job. An anti-snap, anti-pick, anti-drill cylinder from a reputable manufacturer costs relatively little compared to the disruption of a burglary. If you would like a quick assessment as part of a wider lock change Cambridge, or if you want your existing cylinder checked without committing to a replacement, our mobile locksmith team covers Cambridge and the surrounding villages and can usually be with you in about 30 minutes after your call. We confirm an exact up-front price on the phone before anyone sets off, so there are no surprises on the doorstep. The final quote depends on factors including the type of cylinder and door, the time of day, and travel distance — we are transparent about all of it.

Once you have your measurements — say 35/45 or 40/50 — you can order the correct replacement. For most Cambridge homes with uPVC or composite doors, we recommend a TS007 3-star anti-snap cylinder as a minimum. If your door has an older euro cylinder without any snap protection, changing it is one of the most cost-effective security improvements you can make. If you live in a flat on a communal corridor, bear in mind that your managing agent or housing association may have a say over the cylinder specification for the communal entrance, though your individual flat door is usually yours to upgrade freely.

Beyond snapping, good cylinders also resist picking and drilling — two techniques that, while less common than snapping, do occur. A TS007-rated cylinder typically combines anti-snap break points with hardened steel inserts against drilling and security pins against picking, so a single upgrade addresses multiple attack methods at once. If you are dealing with a lock that has already been tampered with, is stiff or difficult to turn, or if you have recently moved into a new property and want to change a lock so previous occupants no longer have a working key, our team handles all of these scenarios as routine work. For anything urgent — a door that will not lock properly late at night, or a cylinder that has partially snapped and left you locked out Cambridge residents can call 01223 912859 at any hour. We operate as a 24 hour locksmith Cambridge wide, seven days a week, including bank holidays.

Chesterton Locksmith is a fully insured, mobile locksmith service operating across Cambridge and the surrounding area, including villages such as Histon, Impington, Fulbourn, and Great Shelford. Our trained team handles a wide range of residential and commercial locksmith work, and because we are mobile, we come to you rather than asking you to travel to a shop. Here is a full picture of what we cover on a daily basis: emergency locksmith Cambridge call-outs, locked-out assistance for houses and flats, uPVC door lock repair Cambridge, euro cylinder replacement, anti-snap cylinder upgrades, TS007 3-star cylinder fitting, 5-lever mortice deadlock installation and repair, Yale-type nightlatch fitting and replacement, multipoint lock repair and replacement, door lock replacement Cambridge wide, lock change Cambridge after a house move or tenancy change, boarding up after forced entry, door alignment and adjustment to cure stiff or misaligned locks, communal entrance lock maintenance for blocks of flats, landlord lock changes between tenancies, letting-agent lock audits, wooden door lock upgrades, composite door lock repair, timber door lock repair, security surveys and advice on BS3621-rated locks, masterkey systems for landlords and managing agents with multiple properties, access control installation for residential and commercial premises, door furniture fitting including handles and escutcheons, emergency out-of-hours call-outs on evenings, weekends, and bank holidays, and general lock maintenance for older properties with worn mechanisms.