They are designed for conveying air in ventilation and air-conditioning.
Made of spirally wound strip of galvanized steel with a thickness from 0.5 to 0.8 mm depending on the diameter or according to customer requirements.

Fittings (elbows, bends, reducers, transitions, tees, S-removal and more. ) is also made of galvanized steel of different thicknesses depending on the perimeter.