The central de-gassing bayonet plug (part# B51210) changes the way the hydrogen gas vents into the atmosphere during the charge cycle.
It expels the gas through the filter (flame arrestor) and then sends the filtered air through the return tubing and away from the
battery.
The filter EX (part# Filter EX) works in conjunction with the central degassing plug to filter the hydrogen gas.
It is used to avoid arcing on the batteries or inside the cells. It is proven and fail-safe.