Knob-operated worm gear adjusts patented butterfly valve, only 2-1/2 turns to full open or close. Controls volume, not air pattern minimum air restriction. Galvanized and unpainted steel damper. Steel ring has brown finish. Includes adjustable handle. Use with 6" ceiling diffuser Model No. ABCDWHO6 (SKU 402613) or 8" ceiling diffuser Model No. ABCDWH08 (SKU 402621).