This set of O-rings contains replacement gaskets to seal the glass tube of a HEATKILLER® Tube series reservoir. 

To alleviate the tolerances in production, there are two different widths of O-rings. These can occur in any combination in your reservoir. 

When replacing the O-rings, you have to make sure to use the same combination of widths that you found when disassembling your reservoir. If there are two different widths, it is irrelevant which one was mounted where. It's just important that the combination is correct.