<p>The plate has a plate body with a frame, and a support plate (3) arranged on the frame. Slots (31) are provided in the support plate for air passage openings. The slots comprise width that is larger than predetermined width (34). Gas supply inserts (4) are provided with a middle piece and a guiding piece. The gas supply inserts with the middle piece are inserted through the slots and are variably positioned with the guiding piece for different constriction of the slots. The inserts are projected at an upper side and a lower side of the support plate.</p>
