How to Measure a Euro Cylinder

A euro cylinder is the oval-shaped barrel that sits inside the lock case on most uPVC and composite front doors across the UK. It is the component your key actually turns. The cylinder is held in place by a single screw through the door faceplate, and that simplicity is both its strength and its weakness. When a cylinder is the wrong size — specifically when it protrudes too far on the outside of the door — a burglar can grip the exposed section with pliers or a cheap tool, snap the barrel in two, and push the door open in under a minute without making much noise. This technique, known as cylinder snapping, accounts for a significant proportion of break-ins on uPVC and composite doors in areas like Slough. A correctly sized, flush-fitting cylinder removes that grip point almost entirely. Add an anti-snap, TS007 3-star rated cylinder and the risk drops further still.

The measurement you are taking is not just about whether the cylinder physically fits in the lock case — it is about making sure nothing sticks out far enough to be attacked. That is why getting the number right before you order a replacement is so important, and why a locksmith carrying out a door lock replacement Slough will always measure before they fit.

You need only a tape measure or a steel rule. Remove the key from the lock and open the door so you can work comfortably. Stand on the inside of the door and look at the cylinder from the edge. You will see that the cylinder passes through the door from the outside thumb-turn or keyhole all the way to the inside thumb-turn. The measurement is taken in two halves, split at the centre screw hole. First, measure from the centre of the fixing screw hole to the outside face of the door — this is the external measurement. Then measure from the centre of the same screw hole to the inside face of the door — this is the internal measurement. Write both figures down in millimetres. A common size on a standard door might be 35mm on the outside and 35mm on the inside, written as 35/35, giving a total length of 70mm. Other very common sizes are 35/45, 40/40, and 45/45, but doors vary, so always measure your own rather than guessing from a neighbour's.

One critical check: now measure how far the cylinder actually protrudes beyond the outer face of the door. On a secure installation, the cylinder face should sit flush with or only very slightly proud of the door surface. If the barrel sticks out more than roughly 3mm beyond the outer face, it is in the vulnerable zone for snapping. This situation is particularly common on older uPVC doors in Slough where the original cylinder has been replaced without careful measurement, or where the door has been adjusted over time and the cylinder not revisited. If yours protrudes noticeably, that is the point to call a professional — a upvc door lock repair Slough job often begins with correcting exactly this issue.

The physics of cylinder snapping are straightforward. Euro cylinders are manufactured with a deliberate weak point just inside the cam — the small rotating piece that operates the lock mechanism. This is a design feature, not a flaw: it means that if someone tries to drill or force the cylinder, it breaks at a point that still keeps the door secure. The problem arises when the outer section of the cylinder is long enough to be gripped from outside. With any rigid lever or tool, an attacker can apply rotational force to the exposed section, shear the cylinder at that weak point, then use a screwdriver to rotate the exposed cam and open the door. The whole process can take less than 30 seconds on a vulnerable door.

The solution has two parts. First, fit a correctly sized cylinder so the external section sits flush with the door. Second, choose a cylinder that carries the TS007 3-star rating or at least anti-snap accreditation — these are engineered with additional internal sacrificial sections that break before the cam is exposed. If you are arranging a lock change Slough, ask specifically for an anti-snap cylinder and confirm the external measurement will be flush once fitted. Streets like Trelawney Avenue in Langley and the terraced roads running off Farnham Road are typical of the housing stock where uPVC doors — and therefore euro cylinders — are the norm, and where getting this detail right genuinely matters.

Measuring your cylinder yourself is straightforward when the door is open and you have easy access. There are situations, however, where measuring becomes the least of your problems. If your key is turning stiffly, the cylinder feels gritty, or you have heard a click or crunch when locking up, do not assume a spot of WD-40 will fix it — a damaged or worn cylinder can fail completely and leave you either locked out or unable to secure the property. If the cylinder has already been tampered with and you can see scratches, tool marks, or the barrel is visibly misaligned, treat it as an emergency: the door may not be as secure as it appears.

Being locked out is another scenario where measuring is irrelevant and speed matters. If you are locked out Slough — whether from a flat in Chalvey, a house in Upton, or a property near Slough Trading Estate — do not try to force entry yourself, and avoid any advice about how to pick a door knob lock or how to pick a lock door knob found on the internet. Attempting to pick or force your own lock without proper training risks damaging the door, the frame, and the cylinder, and can leave the property less secure than before. The legitimate steps are: check for a spare key with a trusted neighbour or family member, check whether a rear or side door is accessible, and if not, call a professional. As a 24 hour locksmith Slough, Langley Locksmith can be with you in around 30 minutes. Call 01753 251949 — we answer every hour of every day, including evenings, weekends, and bank holidays.

Once you have your measurement — say 40/45 for a door where the inside thumb-turn side is a little longer — you can either source a cylinder yourself or ask a locksmith to supply and fit one. If you are arranging this as a planned door lock replacement Slough rather than an emergency call-out, there are a few things worth knowing about how the final price is worked out. The type of cylinder matters: a standard brass cylinder, an anti-snap cylinder, and a high-security TS007 3-star cylinder all sit at different points on the cost scale. The length and profile matter too — most doors in the Slough area take a standard euro profile, but some older or imported doors use different profiles that require specific stock. The time of day affects the quote: an out-of-hours emergency call-out is priced differently from a pre-arranged afternoon appointment. Travel distance from our base in the Langley area plays a small role, as does whether the work involves fitting a cylinder you have supplied or one we bring. We always confirm an exact price before any work starts — there are no surprises on the invoice.

It is also worth noting that fitting a new cylinder is one of the more straightforward lock-related jobs, but it still needs to be done correctly. The fixing screw must be the right length — too short and the cylinder can be pulled out; too long and it may foul the cam. The cylinder must be tested with the door open before the door is closed, and the thumb-turn must operate cleanly from inside. If your door has additional security features like a hook bolt or anti-lift blocks as part of a multipoint locking system, the cylinder replacement needs to be done without disturbing those. A skilled emergency locksmith Slough will check all of this as a matter of course. If you have been wondering how to change a door lock or how to change a lock yourself, a euro cylinder swap is about as approachable as it gets for a confident DIYer — but if there is any doubt, the cost of getting it wrong (a damaged door, a weekend locked out, or a compromised security point) outweighs the saving.

Langley Locksmith covers Slough and the wider area including Langley, Cippenham, Colnbrook, Datchet, Burnham, Taplow, Iver, and Wexham. Our mobile team handles: euro cylinder measurement and replacement, anti-snap cylinder upgrades, TS007 3-star cylinder fitting, uPVC door lock repair, multipoint lock repair and replacement, Yale nightlatch fitting and replacement, 5-lever mortice deadlock installation (BS3621 where insurers require it), composite door lock servicing, door lock-out response, boarding up after a break-in, door frame and keep repair, lock change after a break-in, lock change after a lost key, lock change for new tenants (landlords and letting agents welcome), lock change following a relationship breakdown or change of occupancy, communal door lock repair for blocks of flats, wooden door lock upgrades, door alignment checks (a misaligned door strains the lock), anti-pick cylinder fitting, anti-drill cylinder fitting, anti-bump cylinder fitting, door hinge bolt installation, letterbox restrictor fitting, sash window lock fitting, French door lock repair, patio door lock repair, and security surveys for residential properties. Every job is carried out by an experienced, fully insured locksmith.

Homeowners sometimes ask us about electronic and keypad door locks alongside traditional cylinder questions. If you are trying to work out how to change code on keypad door lock or how to change door lock code after a tenant leaves, the process varies by brand and model — most keypad locks have a programming button inside the battery compartment and require the existing admin code to set a new one. If you have lost the admin code, the lock usually needs to be reset to factory settings using a procedure in the manufacturer's guide, after which a new code can be programmed. If the lock is fully unresponsive, the issue is often a flat battery rather than a fault. We can advise on keypad lock troubleshooting and, where a replacement is needed, can supply and fit a suitable unit. For those asking about how to change code on door lock models without documentation, the most reliable approach is to contact the manufacturer directly or have a locksmith assess whether a reset or full replacement is the more practical route.