Oxygen diffusion stone
2 Micron Stone, 1/2" Diameter 1" Long. 1/4" barb.
Use to aerate wort prior to fermentation. Most common application includes attaching the stone to a 1/4" ID hose from a common (inexpensive) aquarium pump and running it in the wort for 30-60 min.
Should be cleaned and sanitize after each use, and re-sanitized before use.
Note, depending on the environment, some people choose to also use a sanitary air filter (search part number 4984) in the line to the stone.