A double euro cylinder, or key-both-sides cylinder, needs a key to lock and unlock from inside and outside. It's the standard cylinder on most UK front and back doors.
Key both sides or thumb turn?
Key both sides is the safer choice where someone could reach the inside of the lock through a letterbox, cat flap or glass panel, because there's no turn for them to use. If you'd rather lock and unlock from inside without a key, see thumb turn cylinders.
Which double cylinder?
TS007 3-star anti-snap: the Avocet ABS (our recommendation) and the Yale Platinum, plus APECS and SECURIT 3 Star.
Euro cylinders are measured from the central fixing screw to each end, for example 40/50 (40mm inside, 50mm outside). The cylinder should sit flush with the handle or stick out no more than 3mm. See our euro cylinder measuring guide, or browse all euro cylinder locks.
Not sure of your size?
Measure from the centre screw — takes 20 seconds. We'll tell you the exact size to order.
Choose key both sides when the lock sits near a letterbox, cat flap or glazing, because an intruder can't unlock the door by reaching through — there's no thumb turn to twist. It's the standard choice for front doors and any door with glass panels.
Against break-ins near glazing or letterboxes, yes — there's nothing to manipulate from outside. The trade-off is escape: you need a key to get out, so many households keep one in the lock overnight or hang one nearby. For doors away from glass, a thumb turn is a reasonable alternative.
It depends on the cylinder. Models with an anti-lockout or dual-cam feature can be operated even when a key is inserted on the inside — worth choosing if you leave a key in the door overnight. Standard cylinders usually can't; the inside key blocks the outside one.
Measure your existing cylinder from the centre of the fixing hole to each end — for example 35/45. Fit the closest size that leaves the cylinder flush with, or under 3mm proud of, the handle. If in doubt, bring the old cylinder to our Liverpool trade counter and we'll match it.
We stock key both sides cylinders across the range from budget replacements up to TS007 3-Star anti-snap models from Avocet ABS and Yale. For any external door we recommend 3-star protection — snapping remains the most common way uPVC doors are forced.
