A coupler is provided for a power-take-out axle of a gearbox. The coupler includes a coupling flange, a pinion, and a threaded bolt. The coupling flange includes a screw hole and the first curvic coupling member that are arranged in a concentric manner. The pinion is connected to a front end of the coupling flange, and includes a countersink hole, teeth and a second curvic coupling member arranged in concentric manner. The threaded bolt is inserted in the screw hole from the front end of the pinion through the countersink hole. Hence, the pinion and the coupling flange are bonded.