Ingenious Replacement Gear box Door Lock Centre Case 35mm Backset Double SpindleIngenious Gearbox Centre Case 35mm Double Spindle A replacement centre case gearbox for the Ingenious multipoint door lock mechanism. This particular model is intended to replace the 35mm backset double spindle version. If you're having problems with your door lock, the gearbox is almost always the problem and changing it is as simple as removing a few screws. Information Important measurements: 35mm Backset & 92mm PZ Centres This is the mechanism