This model of carbonation cap does everything that regular carbonation caps do but with several added features.
The post on this unique carbonation cap has been machined to fit both the black/liquid and grey/gas ball lock disconnects. This carbonation cap also includes a barb-tail on the underside so you can attach beer line to act as a dip tube.
This allows the carbonation cap to be used in several different ways including:
1. Carbonating
2. Cleaning your beer lines
3. Using it to counter pressure bottle fill PET bottles
From: Kegland
Carbonation And Line Cleaning Cap - Stainless - BrewShop Home Brew Beer Supplies