This is a bottle cap that fits the standard PET soft-drink bottle. It has three 7mm diameter break out pipes to which tubing can be connected; one of the three internal channels also terminates into a pipe allowing tubing to be connected inside the bottle. The cap has a groove that accommodates an O-ring allowing pressure tight sealing. The O-ring has an internal diameter of 22mm and is 2.5mm thick and must be purchased separately.
The intention of this cap is to allow a myriad of uses for PET bottles to the home tinkerer. PET bottles are extremely strong and can cope with quite a modest internal pressure, they are food safe and resistant to most chemicals.