Handheld extruder welding device for welding thermoplastic synthetic materials, including an extrusion screw with an attachment shaft and a device for the axial attachment of the extrusion screw with the attachment shaft to a gear-equipped drive system; where a one-piece gear housing for holding the gear is equipped with a front-side bearing flange for accepting the extrusion screw; where an output shaft arranged in the bearing flange has an output gear attached to it at the cup-side end and has an opening for inserting the attachment shaft; where a two-part annular clamping flange for clamping the extrusion screw in the bearing flange is provided; and where the clamping flange can be placed on the bearing flange from outside and can be clamped. In addition, the clamping flange may contain at least one feed channel for the welding wire. This design offers a compact, stable, and short gear output where the extrusion screw can be exchanged easily.