The Bayliss Mk7 Greenhouse Autovent Is Approximately 29cm Long And Will Lift A Vent Weighing Up To 6kg. It Can Be Set To Start Opening At Any Temperature Between 12-25c, Giving A Maximum Opening Of Approximately 30cm.our Supplier Gives A 2 Year Guarantee On All Replacement Cylinders Although They Should Last 6-10 Yearsimportant To Ensure That Each Cylinder Is Fitted Exactly Parallel To The Window To Avoid Excess Pressure On Sealwill Fit All Greenhouses Except Robinsons Branddrill Holes Are 6cm - 7cm Apartreplacement Cyclinders Also Availableplease Note: Autovents Do Not Fit Our Harrod Superior Greenhousesavailable In Natural Aluminium Finish