The HPA fill nipple uses standard 1/8 inch NPT fitting used on all paintball HPA tanks. This fitting has an internal check valve that only allows air pressure to flow into the bottle, but not escape back out the fill fitting. This fitting on your HPA bottle attaches to a female connection on an HPA fill station, used to fill your paintball tank.

The Lo-Pro style valve has been a more popular replacement option as it does not stick out as far as a standard fill nipple. Some high end bottles come with this style fill nipple standard.