There is described a gluing unit (1) for applying adhesive to a succession of opening devices (3) to be fitted to respective sealed packages of pourable food products, the unit (1) having: conveying means (20) for feeding the opening devices (3) along a path (A); and adhesive dispensing means (21) located along the path (A) and interacting with each opening device (3) on the conveying means (20) to apply the adhesive to a portion (10) of the opening device (3); and the unit (1) being characterized in that the dispensing means (21) are movable parallel to the path (A), so as to increase output of the unit (1).