Weve Found These Bayliss Automatic Greenhouse Vent Openers To Be The Best On The Market And Are Suitable Vents For Both Wooden Or Aluminum Greenhouse Windows And Frames. with The Two Of The Most Important Aspects Of Successful Greenhouse Growing Being Adequate Ventilation And Preventing Excessive Temperatures, The Bayliss Xl Greenhouse Autovents Are Invaluable As They React To Changes In Greenhouse Temperature And Open And Close Vents Accordingly . Please Note That Although The Bayliss Xl Autovent Will Fit The Vast Majority Of Greenhouses, Some Models Of Halls And Robinsons May Require Additional Fixings. We Also Recommend The Bayliss Mk7 Autovent For Use On Any Alton Greenhouse Structure.bayliss Xl Autovent Can Be Simply Clamped Onto Aluminium Greenhouses Without Any Drillingalternatively, Bolt On Using Existing Holes Or Drilled Holesbayliss Xl Greenhouse Autovent Is 28cm Long And Will Lift A Vent Weighing Up To 5.5kg, Or A Vent Approximately 61cm X 76cm (24\" X 30\")opens Approx 30cmsupplier Offers 2 Year Guarantee On Replacement Cylinders But They Should Last Approximately 6-10 Yearsadditional Fixings (not Supplied) May Be Required For Fitting To Some Halls And Robinsons Modelsplease Note: The Autovents Do Not Fit Our Harrod Superior Greenhouses