Here, we can very clearly see the pinhole in the cylinder We can also rather clearly see where the plastic is injected into the mold for the hemisphere. There is also a number embossed into this inner surface.
	In this view, we've cut the majority of the hemisphere away from the cylinder. The cylinder itself extends 2.0 mm into the cavity if the sphere. In the outer surface of the sphere, there is a depression of approximately 1.5 mm from the inner ring at the opening to the floor of the depression. In one hemisphere, there is a tiny pinhole through the floor of the depression, opening into the cavity of the sphere.
	For what it's worth... Professor Frothinphome's description of the pub draught process: First, the conditioned beer is put into the container, along with the Widget device. A small charge of liquid nitrogen in shot into the container. Initially, some of the beer will ice around this charge of nitrogen, insulating it (ever put dry ice in a bucket of water? Same effect. The water ices around the dry ice, substantially slowing its rate of sublimation ) and the container is sealed. As the beer warms on the shelf and the ice capsule melts, the nitrogen becomes gaseous, greatly increasing the pressure inside the container. EVERYTHING feels the pressure--even the Widget. But its walls are are so thick that equalization cannot be attained simply by compressing the widget--beer is forced into the pinhole to equalize pressure with the can, and all is right with the world. Until someone opens the container. Then all hell breaks loose! The pressure in the container drops radically. Well, don't think that Mr. Widget isn't going to follow along! He again sees the pressure differential, and springs into corrective action, jetting gas and beer through that pinhole, much as the infamous "Pocket Beer Engine" does. The result? That wondrous, cascading Guinness head! Bonus question: What purpose does the nitrogen serve in this process--or any other Guinness pour, for that matter?