... company produces steel of 3.3 borosilicate glass sight glasses 1.7,2.0,3.0,3.3,4.0,5.0,6.0,8.0,10.0,12.0,15.0,20.0,25.0 mm thickness, etc ... than test 40Kgf/cm ²Thermal stability:T300 ° CLinear expansion coefficient (0-300 ° C): 3.3 ×10-7 K-1Softening temperature:820°C borosilicate glass