The filter includes: a structure with a C-shaped profile defining side walls and nozzle pipes, each connected to the structure. Each nozzle pipe has a longitudinal axis and an end; a plate connected over a border of the nozzle pipe end to close the nozzle pipe. The plate extends beyond the border. The end of the nozzle pipe is inserted between the side walls of the C-shaped profile. The plate is connected between the side walls of the C-shaped profile. A U-shaped pin defines a first and a second leg, wherein the first leg is inserted in holes of the side walls of the C-shaped profile. The first and the second leg rest on the nozzle pipe and embracing the nozzle pipe. The plate is at an angle (A) greater than 0° with a plane perpendicular to the longitudinal axis of the nozzle pipe. The second leg has a protrusion that rests against the plate.