3"D, PelletVent Wall Thimble, Use To Provide Required 3" Clearance To Combustibles, Fits Between Standard Wall Studs, Comes With An Insulation Ring To Cut Drafts Where The Pipe Slips Through The Thimble, 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.