Fullex XL Door Lock Multi Point Upvc Gearbox Door Lock 35m92mm 62mm Double Spindle92mm Between Centre Of Top Handle To Centre Of Cylinder 62mm Between Centre Of Bottom Handle To Centre Of Cylinder 35mm Backset (this is the size from the front of the lock to centre of they key hole) The gearbox is usually the part that breaks down. To swap the gearbox, remove the screws on the metal strip that hold the gearbox on, remove the gearbox, fit the new gearbox (making sure the metal sliders on the long strip locate into the gearbox) then