Use this airlock where overhead space is limited as it is shorter than our other style of airlock. Originally developed to be used "wet or dry" most brewers do fill will water for use. Does not have a traditional U-bend so cannot be used to indicate if fermenter is sealed or not. Is wider in the stem so can be harder to fit to grommets in lids than other styles. More suitable to be fitted to large rubber bungs as used on carboys.