All Jacoby-Tarbox sight flow indicators and sight windows with flat glass can be supplied with Dual Windows or with UniGlas windows. If your specifications require an FM Approved assembly, then Dual Windows need to be specified. UniGlas is a unique disc where glass and metal are fused into one single disc. A ten to one safety factor is used in this design. UniGlas is the ONLY disc available that may be re-used when an assembly is rebuilt. UniGlas may be re-used because the stress introduced by the bolting is only applied to the metal and not the glass.