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
 

Three tendons (four grooves)
Size:
340 x 34(30) x 17mm 320 x 34(30) x 17mm,
280 x 34(30) x 17mm
250 x 34(30) x 17mm, 218 x 34(30) x 17mm,
190 x 34(30) x 17mm
165 x 34(30) x 17mm, 140 x 34(30) x 17mm,
115 x 34(30) x 17mm
400 x 34 x 17mm,370 x 34 x 17mm
300 x 34 x 17mm
400x 34x 17mm   370x 34 x 17mm    300 x 34 x 17mm
The other size is optional or according to the requirements of customers.
Working temperature: 260 ℃, Working pressure: 4.0MPa

Two tendons (three grooves)
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
280×34×22mm, 280×28×17mm, 250×34×20mm, 250×34×22mm,
The other size is optional or according to the requirements of customers.
Working temperature: 260 ℃, Working pressure: 4.4MPa

Transparent plane
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, 216 x 34 x 17mm
190 x 34 x 17mm, 165 x 34 x 17mm, 215 x 34 x 22mm
218 x 38 x 23mm, 190 x 38 x 23mm, 165 x 38 x 23mm
The other size is optional or according to the requirements of customers.

Working temperature: 260 ℃, Working pressure: 8.0 MPa