Don't have to rely on meshes to cat proof the house. Can open up and let the air and wind flows with the cats staring from the inside without climbing in. The cat will be very angry and will nag at you. To be on the safe side, the gap of the window grilles for cat safety should be around 2 inches. No GST! No additional charges No installation! No delivery! Please do not hesitate to call, SMS or whatsapp Jen hp 81617422