Heat-preserve Internal Joint (HVAC duct ,air conditioner duct) material: gavalnised steel, Stainless Steel. Heat-preserve Internal Joint (HVAC duct ,air conditioner duct) purpose: HVAC, inlet and outlet ... special specification can be made to order. We main products are HVAC fittng, vent duct, ship duct, air duct,aluminum flexible duct, regulating damper, connector, elbow ...