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How to Measure for a New Cylinder

The size that matters is two numbers, not one. A cylinder is measured from the centre of the small fixing screw hole in the middle, out to each end – for example 35/45, which is 80mm overall. The two sides can be different.

Ilan Baroukh By Ilan Baroukh Certified locksmith

You don't need to take the cylinder out to get started

  • Measure the thickness of the door at the cylinder, and how far the cylinder sticks out on each side of the door.
  • Note which side is the outside of the door. If the cylinder has a thumbturn (the small knob), that side is on the inside.
  • If the cylinder sits behind a metal guard or shield on the outside, say so. It changes the size and how far the new one needs to stick out.
  • Not sure? Send a photo of both sides of the cylinder and the edge of the door on WhatsApp with a ruler in the shot. That's usually enough to match the size.

More tips & guides

Lock & Door Tips: How to Spot What's Wrong Key won't turn, key snapped, door only locks when you lift it? How to tell which fault you have, what's safe to try yourself and when to call. Read How to Measure for a 101 Lock (Aluminum Door Mechanism) The slim lock case in the edge of an aluminum door. The three measurements that match a new one, taken without removing the lock. Read