if you tighten the window with gauze or a special plastic grid sold in hardware stores— is well known. However, the existing methods of their attachment^and frame, I think, is far from perfect.
Offer their own, the most convenient option. You need to bind the grid stripe “thistles”, and on the outside of the frame to secure with small nails or glue counterpart of this clasp. This method allows to close the window and remove the protective grid for cleaning of accumulated dust on it.
P. IVANOV, Stupino, Moscow region.