How to Measure a Euro Cylinder

A euro cylinder is the barrel-shaped mechanism that sits inside the lock case on most uPVC and composite front doors across Harrow. It is the part your key turns. If you live in a property on Greenhill Way, a flat off Station Road, or a newer-build house near Harrow-on-the-Hill, there is a very strong chance your front door uses one. The cylinder is held in place by a single screw through the lock case and a cam or tailpiece that connects to the multipoint locking mechanism running up and down the door edge.

Understanding what you are measuring matters because euro cylinders come in a huge range of sizes — typically anywhere from 60 mm to 110 mm in total length. A 70 mm cylinder is not simply a bit shorter than an 80 mm one; fitted in the wrong door, it could leave the spindle misaligned, the cam unable to turn the lock, or — far worse — the outer portion sticking out far enough to be gripped and snapped off with a cheap pair of pliers. That last scenario is not theoretical. Cylinder-snapping is one of the most common methods of forced entry recorded across the London Borough of Harrow.

Remove the door furniture if you can (the handle and the cover plate), but it is not strictly necessary. What you need to find is the centre of the cylinder — the small hole or notch where the fixing screw passes through. This is the reference point for every measurement. Using your tape measure, measure from the outside face of the door to the centre of that fixing screw. Write that number down — this is your external measurement. Then measure from the inside face of the door to the centre of the fixing screw. Write that down too. Add a millimetre or two to each side only if there is a beading strip or decorative cover plate that sits proud of the door face, and account for that in your total. A cylinder is always described as external measurement x internal measurement — so a door that is 40 mm on the outside and 45 mm on the inside takes a 40x45 cylinder, written as 85 mm total.

A few practical checks to make while you are there: open the door and look at the edge. If the existing cylinder protrudes more than 3 mm beyond the face of the lock case or the door face itself, it is in the danger zone. Anti-snap cylinders are designed so that the outer section shears off cleanly before the cam is reached — but only if the cylinder is correctly fitted and not excessively proud. If you are replacing a cylinder as part of a door lock replacement Harrow job, this is the moment to upgrade to a TS007 3-star rated anti-snap cylinder, which satisfies most home insurance requirements and costs little more than a standard one.

Cylinder snapping became widely publicised as a method of burglary because it requires almost no skill and very little time. A burglar uses a screwdriver or similar tool to apply rotational force to the protruding end of the cylinder. If that end sticks out by more than a few millimetres, there is enough leverage to snap the cylinder at its weakest point — usually just inside the door face — exposing the cam and allowing the door to be opened within seconds. Homes across HA1, HA2, and HA3 have been targeted this way, and in most cases the entry point was a standard cylinder fitted slightly too long.

The fix is straightforward: fit the correct-length cylinder so that neither end protrudes unnecessarily, and choose one with an anti-snap design. When Harrow Locksmith carries out a uPVC door lock repair Harrow or a full cylinder change, Andrew measures the door precisely before fitting anything. The replacement cylinder is confirmed flush or no more than 1–2 mm proud on the outside, and the TS007 rating is checked on the product packaging before it goes in. If you are unsure whether your current cylinder is at risk, a quick visual check is all it takes — if you can see more than about 3 mm of cylinder metal beyond the door face without a protective escutcheon covering it, it is worth getting it looked at.

Once you have your measurements, you need to choose the right grade of cylinder. For most front doors in Harrow, a TS007 3-star cylinder is the sensible baseline. The TS007 standard covers three threats: snapping, picking, and drilling. A 3-star single cylinder achieves this on its own; a 1-star cylinder paired with a 2-star handle can also reach the same overall rating, which is worth knowing if you are replacing only the barrel. Many insurers now specify anti-snap cylinders as a condition of cover, so fitting one is not just about security — it protects your policy.

If the door is a timber door with a 5-lever mortice deadlock rather than a euro cylinder, the measurement process is different and the product range is entirely separate — that lock uses a key rather than a cylinder barrel. If you are unsure what type of lock you have, or if the cylinder is already damaged, jammed, or the key is stuck inside it, do not force it. Forcing a compromised cylinder can push broken components further into the lock case and make a straightforward cylinder change into a more involved job. Instead, call 020 3750 2226 and Andrew will talk you through what he can see from your description before coming out. As a 24 hour locksmith Harrow residents can rely on, we confirm the full up-front price on the phone before anyone travels — the final quote accounts for the cylinder type needed, travel from our current location, and the time of day, so there are no surprises on the doorstep.

Sometimes measuring is not the priority. If you are locked out Harrow, standing on your doorstep at midnight, or you have just come home to find a cylinder has been tampered with and your door will not open, the measurement conversation can wait. What matters is getting back inside safely. Andrew carries a range of the most common cylinder sizes and grades as standard, so in the majority of door lock replacement Harrow call-outs, the right cylinder is on the van and the job is completed in a single visit.

As a 5-star rated emergency locksmith Harrow, Andrew works on his own — you deal with one person from the first call to the moment the door closes behind you. He is known for being punctual, for quoting before charging, and for not leaving until the door locks and unlocks cleanly. If your situation is urgent — a broken key in the lock, a snapped cylinder, a door that will not close properly after an attempted break-in — call 020 3750 2226 now. We answer 24/7, including evenings, weekends, and bank holidays, and we are usually with you in about 30 minutes.

To recap the process: measure from the outside face of the door to the centre of the fixing screw, then repeat from the inside face. Write both numbers down in the format external x internal. Check the existing cylinder for any visible overhang beyond the door face. If you are replacing it, choose a TS007 3-star anti-snap cylinder of the correct size. When in doubt — particularly if the door is already failing to open or close, or if there are signs of tampering — do not attempt to force anything. A professional cylinder change is a quick job done right; a forced or incorrectly-fitted cylinder can compromise the entire door frame.

Harrow Locksmith covers the full Harrow area — from the town centre around St Ann's Road to the quieter residential streets in Harrow Weald, Hatch End, Pinner, and Rayners Lane. Whether you need a straightforward cylinder swap or a full door lock replacement Harrow job following a break-in attempt, the process is the same: one call, one visit, one clear price agreed before work starts. Call 020 3750 2226 — we answer 24/7.