3" To 4", Pellet Vent Appliance Pipe Adapter, Used To Attach Outlet When Increasing To 4" Pellet Vent, On Venting Stoves Above 4,000'. Must Seal Adapter To Appliance With High Temperature Sealant, Designed For Stoves That Burn Wood Pellets, Patent Pending Venting For Stoves & Inserts That Use Wood Pellets, UL Listed For 3" Clearance To Combustibles In USA & Canada.