tempered borosilicate sight glass -use for fireplace,light,or sightlevelglass -many size available -withstand 600 C ... ,tank sight glass, flange sight glass,boiler sight glass,-for light,machine etc-flat,clear,smooth,high quality-withstand 600 ... are available-OEM is availableContact Huhu for more information and good price ,15953257075 for light use and sight glass use tempered borosilicate sight glass