Sight Glass  is a glass which suitable for industrial applications due to resilience have mechanical 5 X (five times) stronger than normal glass with a thick & the same size.
Sight Glass also have resistance to high temperature varies up to 400 degrees centigrade which is also dependent on glass thickness.
Options Baeco Sight Glass thickness from 3 mm thick to 25 mm thick with a variety of forms such as the desired square, rounded, oval, etc. ..