Chamber style airlock. Fill chamber with water over a sink; insert top piece (lid) overtop. Water will overflow from the chamber. Now it’s ready to insert through the grommet. Top up with water if water level falls below half. Not appropriate for room-temperature phase in jars 3/4 L and larger. The 1/2 L jar can use the mini airlock throughout the fermentation process.
Saves vertical height during the second fermentation stage in a fridge or root cellar. Simply prepare mini airlock; remove the 3-piece airlock and quickly, almost seamlessly, insert the mini airlock through the grommet. Minimize the amount of air that enters the jar during this airlock swap.
Allows a visual passage of gas pressure to escape but allows no air to enter.