If your uPVC door lock has broken it can be a daunting task to try and figure out which gearbox you need as even if you find the correct manufacturer and a similar looking gearbox there are many other variables like the back set and spindle operation. This is a complete guide on how to figure out what gearbox you need.
Firstly, What Is A Backset?
The backset of a door lock gearbox if the distance from the front of the gearbox to the centre of the spindle hole as shown in the image below.
The most popular backsets are 30mm, 35mm, 45mm and 55mm.
What is a PZ measurement?
The PZ is the distance from the centre of the spindle hole to the centre of the euro cylinder hole as shown in the image below.
In the example above the gearbox is a twin spindle gearbox which means it has multiple PZ measurements. So in the example above you would need a 92/62pz gearbox.
What is a Spindle Hole / Spindle Operation?
The spindle hole is where the spindle from the door handle goes through the gearbox which operates the door lock. The spindle operation is the spindle hole layout, as shown in the example below a single spindle will have one spindle hole and a twin spindle will have two spindle holes.
There is also a 3rd operation which is a split spindle gearbox, this will look like a single spindle gearbox but will operate like a twin spindle. The difference between a single spindle and a twin spindle gearbox is that when you pull the handle up from the outside it will lock the door. Where as with a single spindle you need to pull the handle up and lock the euro cylinder.
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If you still can't figure out what gearbox you need please contact us on the live chat which can be found in the bottom right corner of this website. Upload a picture of your gearbox and we will be able to find the exact gearbox for you.