How to Measure a Euro Cylinder

A euro cylinder is the oval-shaped barrel that sits inside the lock housing on most modern uPVC and composite front doors across Northampton and the surrounding area — the kind of door you will find on new-build estates off Upton Way, on terraced houses in Kingsthorpe, and on flats throughout the town centre. When you push your key in, the cylinder is the part doing the work. It is held in place by a single central screw through the door handle faceplate, which is why it can be removed quickly — legitimately by a locksmith, and illegitimately by someone with a pair of grips and thirty seconds.

The cylinder has two halves: the external half (outside the door, facing the street) and the internal half (inside your home). Each half is measured separately from the centre of the fixing screw hole outward to the end of the barrel. Those two numbers, written as something like 35/45 or 40/40, are what you need before ordering or requesting a replacement. Getting one side even five millimetres longer than it needs to be is not a minor inconvenience — it is the difference between a secure door and one that is vulnerable to cylinder snapping, one of the most common break-in methods reported across Northampton.

Remove the door handle faceplate screw (the single screw in the centre of the handle) so you can see the cylinder clearly, but you do not need to remove the cylinder itself to measure it. Take a tape measure and find the centre point of the fixing screw hole — this is your reference point for both measurements. Measure from that centre point outward to the very end of the cylinder on the external side of the door. Write that number down. Then measure from the same centre point to the end of the cylinder on the internal side of the door. You now have your two figures. If the external measurement is 35 mm and the internal is 45 mm, your cylinder is a 35/45. Always double-check by measuring with the door open so the tape sits flush against the barrel without the door frame getting in the way.

One common mistake homeowners make is measuring the total length of the cylinder and trying to split it in half — this only works if you happen to have a perfectly symmetrical lock, which many people do not. Measure each side independently and you will always get the right result. It is also worth checking whether the cylinder sits flush with — or proud of — the door furniture (the metal escutcheon plate around the barrel). If any part of the cylinder protrudes beyond that plate, read the next section carefully before you buy anything.

Cylinder snapping is not a dramatic, loud forced entry. It is quiet, fast, and brutally effective. A burglar applies lateral force to the exposed section of the cylinder — the part sticking out beyond the door furniture — and the barrel snaps at its weakest point, typically around the central cam. Once snapped, the internal mechanism is exposed and the door opens in seconds. Research from police forces across the UK, including reports relevant to Northamptonshire, consistently highlights snapping as a primary method used against uPVC doors precisely because so many cylinders are fitted incorrectly or replaced with the wrong size.

The fix is straightforward once you understand the measurement. Your replacement cylinder should sit flush with the escutcheon plate or no more than one or two millimetres proud of it. If your current cylinder protrudes by five millimetres or more, you are exposed. When arranging a lock change Northampton residents often ask whether a standard cylinder will do — the honest answer is that for most front doors, a TS007 3-star anti-snap cylinder is the right choice. These are engineered with a sacrificial snap point away from the cam, meaning even if a burglar snaps the external end, the door remains locked. Many home insurers now expect this standard on uPVC and composite doors, so it is worth checking your policy wording. If you are unsure whether your current cylinder is anti-snap rated or want a professional assessment, call 01604 913072 — we cover Northampton and the surrounding villages around the clock.

Once you have your measurements, you need to decide on the specification — not just the size. For a standard uPVC door lock repair Northampton homeowners should look for cylinders carrying the TS007 3-star kitemark, which is the British Standard that tests resistance to snapping, drilling, picking, and bumping. Some cylinders achieve 3-star rating through a combination of products — for example, a 1-star cylinder paired with a 2-star door handle — but a standalone 3-star cylinder is the simplest and most reliable solution. Avoid buying on price alone; a cylinder that fails a forced-entry test is worth nothing regardless of what it cost.

It is also worth knowing that not all euro cylinders are identical in profile. Most uPVC doors in Northampton use a standard euro profile, but some older or continental-spec doors use a different oval or round profile entirely. If you are unsure, photograph the existing cylinder alongside your measurements before purchasing. A trained locksmith can confirm the right specification on-site and source the correct part, which is often faster than returning a wrong-sized cylinder to a shop. For door lock replacement Northampton wide, we carry a range of anti-snap cylinders in our van and can fit one the same visit, whatever time of day or night you call.

Measuring a cylinder is genuinely a two-minute DIY task. Replacing one is also manageable for a confident homeowner if the door is functioning normally and the cylinder slides out cleanly after the retaining screw is removed. Where things go wrong is when the cylinder is damaged, corroded, or has already been partially snapped — in those cases, forcing the removal can damage the door frame, the multipoint lock mechanism, or leave you locked out Northampton-style: standing on the doorstep with no way back in. If the cylinder is stiff, the key is not turning smoothly, or there is any visible damage to the barrel, stop and call a professional.

As an emergency locksmith Northampton, our team at Duston Locksmith deals with snapped and damaged cylinders regularly — it is one of the most common call-outs we attend across NN1 through to the villages around Northampton. As a 24 hour locksmith Northampton residents can rely on, we are available every evening, every weekend, and every bank holiday. When you call 01604 913072, we will confirm an exact price before anyone leaves, so you know what to expect — the final quote depends on factors such as the type of cylinder needed, any additional work on the door frame, and the time of call. We then send a locksmith straight away and are usually with you in about 30 minutes.

Euro cylinders are found on most uPVC and composite doors, but they are not the only lock type you will encounter. Many Northampton homes — particularly Victorian and Edwardian terraces in areas like St James and Semilong — have timber front doors fitted with a Yale-type nightlatch and a 5-lever mortice deadlock. Insurers often ask for the mortice deadlock to meet BS3621, which covers pick and drill resistance. These locks do not involve a euro cylinder at all; they use a different key and a different fitting process, so measuring a euro cylinder is not relevant to them.

If you are unsure what type of lock is on your door, the simplest way to tell is to look at the keyhole. A euro cylinder has a keyhole that sits inside an oval barrel protruding slightly from the door face. A Yale nightlatch has a small circular keyhole on a round cylinder near the top of the door. A mortice deadlock has a keyhole set into the door itself with no protruding barrel. Knowing which type you have determines everything about how it is measured, priced, and replaced — and our team is always happy to advise over the phone before any visit is booked.