Square to round duct adapter, 100 mm
A transition piece that connects a 100 mm round ventilation hose to a 110 x 110 mm square wall grille or fan housing, common in bathroom extract fans and small workshop ventilation. The round end is a 99.6 mm spigot 40 mm long that fits inside the hose, and the square end is a socket with a 20 mm flange carrying four 4.5 mm screw holes. A 40 mm morphing section with 2 mm walls keeps airflow smooth, and printing with the flange down needs no supports.
Duct sizes and grille openings never quite match the parts in the shop, but SpeakCAD draws the transition to your two measurements and the depth you have behind the wall. Preview free in your browser and ask for a 45-degree offset, a longer spigot or a gasket groove.
Design a square-to-round duct adapter. Square end 110x110 mm socket 15 mm deep with a 20 mm wide flange and four 4.5 mm holes at 130 mm spacing. Round spigot 99.6 mm outer diameter, 40 mm long. Smooth lofted transition 40 mm long, 2 mm walls throughout.