This is a pair of drill-chuck adapters for Medela baby bottle lids: one for the older design that is streamlined, and one for the newer 'wavy' fashion. Spinning the bottle in hot water makes it warm up considerably quicker than simply letting it sit, and in addition, it keeps the milk at a uniform temperature, even in really hot water. It does not cause froth or bubbles.
To use it, simply cut your chilly milk bottle into your 3/8" variable speed drill and spin the bottle in a bowl or cup of hot water at reasonable speed, 10 seconds on, 10 seconds away. The aim would be to get as much difference as possible between the speed of the bottle and the speed of the milk. The milk will only spin up to exactly the same rate as the bottle if you whirl it too long at once and you will lose some efficacy.
The versions contain baked-in supports for the shaft that is easily removed with flush cutters or a hobby knife. They are optimized for a 0.4mm extrusion width.