70 Is the Total, Not the Split

A euro-profile cylinder is described by one number in almost every catalogue in the industry, ours included: 45, 50, 55, 60, 65, 70, 80. That number is the overall length in millimetres, measured end to end. It is genuinely useful and it is genuinely incomplete, because two cylinders of exactly 70mm can be completely different parts.

The cam sits somewhere along that length — the little bar that turns and throws the bolt, driven by the fixing screw that passes through it. The length is divided either side of that cam, and the two halves are quoted as a split: 35/35, 30/40, 40/30. All three are 70mm cylinders. Only one of them fits your door.

Which one depends on what is in front of and behind the lock case. Measure from the fixing-screw hole in the edge of the door — that is the cam centre — outward to the finished face on each side, and include everything the cylinder has to pass through: the door leaf, any escutcheon or rose, a decorative plate, a security rosette. The outside measurement is the outside half; the inside measurement is the inside half. Round each up to the next 5mm that a cylinder is actually made in.

Getting it short is obvious on site: the key will not enter far enough, or it enters and will not turn because the cam cannot clear. Getting it long is the more expensive mistake, because it looks fine. A cylinder standing proud of the escutcheon is the single easiest thing on a door to attack — it gives a tool something to grip and lever against — and on an external door that projection is what an insurer or a specification will pick up on. As a working rule, keep projection to about 3mm or less on the outside face.

This is also why a cylinder is the wrong item to standardise across a mixed order. Doors on one project are rarely one thickness: a 40mm internal leaf, a 45mm entrance leaf and a glazed screen with a 10mm patch fitting all take different splits, and a pallet of one size means somebody on site is going to force something.

Here is the part of this we should say plainly about our own catalogue. Our cylinder pages publish the overall length — 45mm, 47mm, 54mm, 56mm, 65mm, 70mm, 80mm — the material, the finish options and the key count. They do not publish the split, because the split is an order variable rather than a property of the model. We would rather say that than print a default like 35/35 that would be right often enough to be believed and wrong often enough to cost somebody a container.

So the practical route is short. Tell us the door thickness and what is mounted on each face, and our engineering desk will come back with the split, or confirm the one you have specified. If you already work in splits, send them as splits — 30/40 outside/inside is unambiguous in a way that "70mm" is not. Either way, say which side is outside; a 30/40 and a 40/30 are the same cylinder installed backwards, and backwards means the reinforced half is facing the wrong way.

One last thing worth confirming at the same time, because it costs nothing to ask and it is the second most common cylinder omission: keying. Our cylinders ship keyed to differ with three keys as standard, and five is available. Keyed alike within a group, or a master key suite across a building, is a decision that has to be made before the cylinders are pinned — not after they arrive.