The invention relates to a device and a method for friction stir welding materials of different thicknesses and that have fillet welds, comprising the following features: a) a receiver panel (1) that has a drive head (2) and a welding shoe (4) that has a pin bearing, said welding shoe (4) being selected and inserted according to whether it is being used with materials of different thicknesses or with materials that have fillet welds, b) the longitudinal axis of the spindle bearing being at an incline of an angle between 0 and 5 degrees relative to the vertical line; the transverse incline being 0 degrees for the fillet weld shoe (4), and c) when the welding pin (6) is exchanged, the length of the welding pin (6) being adjusted using an adjustment element (12) and the position of the counter-bearing of the welding pin (6) being adjusted using an adjustable pin stop (19) and, in the case of the pin stop (19), additionally secured by an adjustment screw (20).