It is the most important lock you have probably never thought about: the brass barrel sitting behind the handle of nearly every uPVC and composite door in the country. The euro cylinder is the part that actually does the securing — and, not coincidentally, the part a burglar attacks first. This guide explains what it is, how to identify and measure the one on your door, the types you will meet, and why it is the single component most worth spending money on.
A euro cylinder is a standardised, pear-shaped lock barrel that the key turns. As the key rotates, a small cam on the cylinder drives the door’s multipoint mechanism — the hooks and bolts running up and down the door edge. Because the shape is standardised, one cylinder design fits the vast majority of modern doors. The crucial thing to understand is that on a uPVC or composite door, the cylinder is the security: the rest of the multipoint is just metal that does what the cylinder tells it. Defeat the cylinder and the door is open.
Euro cylinders come in a few configurations, and knowing yours helps:
Cylinders are sized by measuring from the central screw hole to each end — for example 35/35 or 40/55 — and getting it right matters for more than fit. A cylinder that protrudes more than a few millimetres beyond the handle hands a burglar the leverage they need to snap it. The correct cylinder sits as close to flush as possible. If you are replacing one, measure each side separately from the centre screw and match it, rather than guessing — a cylinder that sticks out is a weakness no matter how good the lock.
Look at your door from the side. If the cylinder pokes out past the handle by more than about 3 mm, it is both the wrong size and a snapping target — worth correcting whether or not anything else is wrong.
If you spend on one thing, spend it here. A cheap cylinder is exactly why lock snapping still works; a properly rated one defeats it. Look for the marks that prove independent testing — a TS007 3-star or SS312 Diamond anti-snap cylinder — which we explain in full in our guides to anti-snap locks and lock security grades. For businesses, landlords or anyone wanting to control who can copy a key, a restricted or patented key system adds another layer, which we cover under master key systems.
Here is the good news that surprises people: you almost never need a whole new lock. Because the cylinder is a self-contained part, a locksmith simply unscrews the old one and fits a new one — upgrading your security, or giving you new keys, in minutes and for a modest cost. It is the same quick swap that follows losing your keys or moving house. Our guide to the cost of changing locks sets out what to expect.
A named, vetted master locksmith covers your area — no call-out fee.
Getting the cylinder right — the correct size, sitting flush, and properly rated against snapping — is one of the highest-value, lowest-cost things you can do for your door. Every LocksmithLocal locksmith can measure your door, supply and fit an anti-snap euro cylinder, and key several doors alike if you want one key for the lot. Find your local locksmith to get it sorted.
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