High-security Euro profile cylinders.

What a Euro cylinder is

A Euro profile cylinder is the barrel that sits inside a Euro-spec lock case — the standard on most modern doors in the UK and much of Europe. When people say they are "changing the lock", they almost always mean replacing this cylinder. Swapping it is a five-minute job with a single screw, and it re-keys the door to a new set of keys.

Measure before you buy

A Euro cylinder is measured from the centre screw hole outwards on each side — for example 35/35 means 35mm each side. The two halves differ on doors with a handle on one side and a thumb-turn on the other. Measuring wrong is the single most common reason a cylinder will not fit: measure both sides, including any door furniture that sits proud of the door.

Security features worth having

• Anti-snap — a sacrificial section snaps off so the lock cannot be gripped and twisted out.
• Anti-drill — hardened pins inside the barrel resist drilling.
• Anti-pick and anti-bump — security pins defeat the two fastest covert attacks.
• Keyed alike — match one key to several doors, handy for a house with a back door and a shed.

When to replace a cylinder

Replace it when you move into a new home, when keys are lost or unreturned, after a break-in, or when you add a door handled by the same key. A good cylinder is one of the cheapest real security upgrades on a home, and one of the quickest to fit.

Common sizes and how to pick

Euro cylinders come in paired lengths such as 30/30, 35/35, 40/50 and 45/55. The number before the slash is the inside length and the number after is the outside, measured from the centre fixing hole. A door with a thumb-turn usually needs a shorter inside and a longer outside; a door with handles both sides is often symmetrical. When in doubt, take the old cylinder out and measure it — it is the only measurement that cannot be wrong.

Keyed alike across several doors

If one key should open the front door, the back door and the shed, order cylinders keyed alike. This is a genuine convenience, not a gimmick: it removes the bunch of keys people otherwise carry and the risk of leaving the wrong one behind. Buy the set together so the keys are cut to the same profile.

Fitting a new cylinder

Remove the single retaining screw on the lock case, slide the old cylinder out, slide the new one in, and refit the screw. Check the cam turns freely in both directions, then test the key from both sides. If the cylinder sits proud of the door, fit a security escutcheon or a cylinder guard to protect it from snapping.

Frequently asked

How do I measure a Euro cylinder? Measure from the centre screw to each end of the barrel, in millimetres, and note the two lengths separately.

Can I fit it myself? Yes — one retaining screw holds the cylinder in the lock case; no special tools needed.

What is anti-snap? A design that deliberately breaks at a defined point so a thief cannot twist the barrel out of the door.