This is a pair of drill-chuck adapters for Medela baby bottle lids: one for the older compact style, and one for the newer 'wavy' style. Spinning the bottle in hot water makes it warm up much faster than just letting it sit, and it also keeps the milk at a more uniform temperature, even in very hot water. It doesn't cause bubbles or froth.
To use it, just clip your cold milk bottle into your 3/8" variable speed drill and spin the bottle in a bowl or cup of hot water at moderate speed, 10 seconds on, 10 seconds off. The goal is to get as much difference as possible between the speed of the milk and the speed of the bottle. If you spin it too long at once, the milk will just spin up to the same speed as the bottle and you'll lose some efficiency.
The models include baked-in supports for the shaft that can be easily removed with flush cutters or a hobby knife. They're optimized for a 0.4mm extrusion width.