Yale Lockmaster Twin Cam Hookbolt Gearbox Yale Lockmaster Twin Cam Hookbolt Gearbox. The Gearbox is the part that is most likely to be at fault when the door lock fails and becomes unusable. Replacing the gearbox is cost effective, as it saves having to buy a complete new door lock. Should you need any help in measuring or fitting any of our products, please contact us Centre: 62/92mm Gearbox Backset: 35mm Case Height: 227mm Case Width: 47mm Operation: Twin Spindle
