Features: 1) Outer tube diameter: 47 / 58mm 2) Inner tube diameter: 37 / 47mm 3) Glass thickness: 1.6mm 4) Length: 1.5 / 1.8m 5) Material: borosilicate glass 3.3 6) Absorptive coating: graded Al-N / Al 7) Vacuum: 8) Absorptance: >92% (AM1.5) 9) Emittance: 10) Thermal expansion: 3.3 x 10 - 6°C 11) Stagnation temperature: > 200°C 12) Heat loss: 13) Maximum strength: 0.8MPa 14) Hailstone resistance: up to 25mm in diameter