Dont let the usual magnified FT images fool you these things are tiny, i personally use mine to extend the 510 positive pin for hybrid connections. Just remove the pin and slide one of these down the thread, screw it back in and double check nothing is touching the atomiser body so you dont get a short, it is rubber so will perish so i change mine out every couple of months to be safe.

If memory also serves me right i originally grabbed some to seal my KF Lite filling screw, but later moved on to use nylon screws which were much better.

Hope this helps