... 3)ALN/AL-SS/CU Coating 4)Long life-span Glass Vacuum Tube :Certifactes: CE, ISO9001; CCCSpecification:1.Outer Diameter /Inner Diameter : Φ47 ... /47mm ; Φ70/58mm2.Length of Tube : 1500mm, 1800mm, 2000mm, 2100mm3.Material: Borosilicate glass 3.3 , Thickness of tube:1.6± 0.1mm,2 ... %(80 º C± 5º C)8.Coefficient of Average Heat Loss: 0.6-0.7W/(m2 º9. 15year life-span10.10years warranty Glass vacuum tube