New silicon fill hole plugs. These are made from high temperature silicon so they can be left installed while vaping! They prevent e-juice from poring through the wick when the AC9 is upside down. Great to have if you carry the AC9 around a lot.
If you're going to keep the plug in while vaping please note that wicking performance will be reduced, as such you may need to tilt the atty. I've used the AC9 for a week now with the plug installed and it wicks fine, just not quite as good as without the plug.
These come 2 per pack.