In article ,
"Peter Andrews" writes:
What sort of glass should I use to replace a broken sight glass (where you
look to see if the flame is alight) it's about 3" x 2". The burner is a
Waterbury of indeterminate age.

I went to a glass shop and asked for a piece. I don't know what type
of glass it was, but they had to order a piece -- wasn't what they
normally stocked. That piece lasted several years until I chucked
the gas heater out. The proper pieces ordered from the manufacturer
(Drugasar) only lasted about a year before cracking. My heater used
two of them, about half the size of your piece.

--
Andrew Gabriel