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How to Measure for a 101 Lock (Aluminum Door Mechanism)

The 101 is the slim lock case inside the edge of an aluminum door. Three measurements match a new one to your door, and all of them are on the metal strip on the edge of the door.

Ilan Baroukh By Ilan Baroukh Certified locksmith

The three measurements

  • Backset: the distance from the face of the strip to the centre of the cylinder hole. On aluminum doors it's usually 20, 25, 30 or 35mm. This is the one that has to be right.
  • The strip itself: its length and width, and the distance between the screw holes.
  • What sticks out of the lock: a hook that catches behind the frame (sliding doors), a latch, a roller, or a straight bolt (hinged doors).
  • Also check the cylinder shape: standard "euro" or oval – they don't interchange.

You don't need to take the lock out

Open the door and measure the strip and the holes on the edge. A photo of the edge of the open door, plus one of the lock from the side with a ruler in shot, sent on WhatsApp, is usually enough to match it.

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 New Cylinder A cylinder size is two numbers, not one. How to measure yours without taking it out, and what to note before you replace it. Read