This thicker Lid O-Ring is suited to FermZilla Conical and All Rounder Models. All future models produced after 25/12/2019 to 01/01/2023 will have these O-Rings as standard. 

If you have a brown O-Ring, this is a newer material that is softer and easier to fit. All units manufactured after 01/01/2023 will have this Brown O-Ring as standard

If you are experiencing leaking from the top lid section, this slightly thicker O-Ring will aid in resolving said leaking. To perform a leak test please remember to have the unit free of any liquid as that will absorb CO2.
If you are able to show us with a short video or photos that your unit is leaking from the lid. We will replace said O-Ring for free under warranty via mail.