Duct liner pins is a insulation fastener that is used for fastening the duct liner to the inside sheet metal of air duct,Website:http://www.insulationpin.net, they are designed to work with the auto-feed weld machine. MaterialLow carbon steelPlatingZinc platingSizeWasher diameter: 1"Pin diameter: 10GA( 3.4mm)Length1/2" 3/4" 1"  1-1/8" 1-1/2" 2" 3" 4"Application