How to Measure a Euro Cylinder

A euro cylinder — sometimes called a barrel lock or euro profile cylinder — is the oval-shaped locking mechanism fitted inside the lock case on most uPVC and composite doors. You will usually see a keyhole on the outside, a small thumb-turn or second keyhole on the inside, and a visible metal body running through the door. They are extremely common on front and back doors across Sidcup and the wider DA14 and DA15 areas, particularly on uPVC doors fitted to 1990s and 2000s housing estates and on modern composite doors on newer builds along Sidcup High Street and surrounding roads.

Euro cylinders are measured in millimetres, with the total length split into two figures: the external measurement (outside face of the door to the centre of the fixing screw hole) and the internal measurement (inside face of the door to the centre of the fixing screw hole). You will often see these written as, for example, 35/45 or 40/40. The two numbers always add up to the total length of the cylinder. Getting both figures right is essential — this is not a component where close enough will do.

You will need a metal tape measure or a steel ruler — a fabric tape measure can flex and give you an inaccurate reading. Open the door fully so you can work comfortably. First, locate the single fixing screw on the edge (the door stave) — this is usually a small cross-head or Torx screw on the edge of the door, roughly in the centre of the lock case. Remove it and keep it somewhere safe. Now close the door. On the face of the door (outside), measure from the outer edge of the cylinder to the centre of the screw hole — this is your external figure. Then measure from the inner edge of the cylinder (inside the flat or house) to the same central screw hole — this is your internal figure. Write both numbers down. If your door is 70 mm thick and the cylinder sits flush, a 35/35 cylinder is a typical result, but many uPVC front doors need a 35/45 or 40/45, so always measure rather than guess.

One important note: measure to the centre of the screw hole, not the edge of the cylinder body. The fixing screw passes through a cam slot in the cylinder at the centre point, and that is the reference dimension the manufacturer uses. If your tape measure only shows imperial markings, convert carefully — a 35 mm external measurement is roughly 1 and three-eighths of an inch, but buying in millimetres from a UK supplier is far simpler. If the cylinder is already damaged or the screw has sheared, do not force anything — call a professional locksmith Sidcup team to assess it safely.

Here is the part that many homeowners in Sidcup and across the Bexley borough do not realise until it is too late. If your euro cylinder protrudes more than three millimetres beyond the face of the door furniture (the external handle plate or escutcheon), it is vulnerable to cylinder snapping. This is not a theoretical risk — it is a well-documented method of forced entry that takes a burglar under twenty seconds with an ordinary adjustable wrench or large pliers. They grip the protruding section, apply sideways force, snap the cylinder, and use a screwdriver to operate the remaining stump. No noise, no broken glass, no kicked-in door.

This is why measuring your cylinder correctly before buying a replacement matters so much. A cylinder that is too long on the outside — say a 50/35 fitted where a 35/35 belongs — creates exactly this vulnerability. When you replace your cylinder, the outer face should sit flush with, or no more than three millimetres proud of, the external handle plate. Additionally, the replacement cylinder should ideally carry a TS007 3-star rating or be paired with an anti-snap door handle and anti-pick pins. If you are unsure whether your current cylinder is at risk, a quick door lock replacement Sidcup inspection by our team can tell you in minutes. You can reach us at 020 3757 5665 — we are available around the clock.

Once you have your two measurements, you need to choose a cylinder that fits and that actually improves your security. The TS007 standard is the UK's leading performance specification for euro cylinders, covering resistance to snapping, picking, drilling, and bumping. A 3-star TS007 cylinder achieves the highest rating on its own. A 1-star cylinder combined with a 2-star handle can also achieve the full rating — but the components must be tested together as a set, so check the manufacturer's documentation carefully.

For uPVC door lock repair Sidcup work, we typically fit anti-snap cylinders with a sacrificial snap-off section engineered into the external portion. When a burglar applies force, the outer section breaks away deliberately — but the inner section remains locked, with no cam or mechanism exposed. This design is now widely regarded as the minimum acceptable standard for any euro cylinder on a main entrance door. If your insurer specifies BS3621 (which applies to mortice deadlocks rather than euro cylinders), ask them specifically whether they also require a TS007-rated cylinder — many household policies in Sidcup and the surrounding DA postcode area now do. We never carry out unnecessary work, so if your existing cylinder is the correct size and in good condition, we will tell you so honestly rather than recommending a replacement you do not need.

Measuring and ordering a euro cylinder yourself is perfectly reasonable if the existing lock is working, the door opens normally, and you simply want to upgrade security or change the lock after moving into a new property (always a sensible step — you have no way of knowing how many keys are in circulation). However, there are situations where calling a 24 hour locksmith Sidcup is the right move rather than attempting to handle it yourself. If you are locked out Sidcup of your property and the cylinder has failed or been damaged, do not attempt to pick or force the lock — aside from the risk of further damage, you could cause the door to drop out of alignment on a uPVC frame, which is a costly repair. Instead, check whether a window is on the latch, whether a neighbour or letting agent holds a spare key, or whether there is a back door you can access lawfully. If none of those options apply, call us.

Similarly, if your euro cylinder has already been partially snapped — perhaps you noticed the door felt loose, or you can see the outer section has shifted — stop using the door and call us immediately. A partially compromised cylinder can fail completely at an inconvenient moment, or leave the property insecure overnight. We send a locksmith straight away and are usually with you in about 30 minutes across Sidcup, Foots Cray, Blackfen, and the surrounding area. The price is confirmed with you on the phone before anyone sets off — the final quote depends on factors including the type of lock, the cylinder specification needed, the time of day, and travel distance, but there are no hidden additions once we have agreed a figure. Call us on 020 3757 5665 any time, including evenings, weekends, and bank holidays.