It's made from Borosilicate, it is used in lever gauge in boiler for water position.
It is also named: Reflex Gauge Glass, Sight glass, Reflex Glasses
Reflex sight glass, Spares For level Gauge
The category is as follows:
1) Three tendons (four grooves)
2) Two tendons (three grooves)
3) Plan transparent
Size:
340 x 34 x 17mm 320 x 34 x 17mm,280 x 34 x 17mm
250 x 34 x 17mm,218 x 34 x 17mm,190 x 34 x 17mm
165 x 34 x 17mm,140 x 34x 17mm,115 x 34 x 17mm
The other size is optional or according to the requirements of the clients.