These are standard clear plastic airlocks that fit standard rubber “gum” stopper.
These properly fit any stopper that has a 3/8″ hole drilled in it to accept a standard airlock.
They also fit rubber grommets with 3/8″ inner diameter opening… Like the ones that come with a whole host of beer and wine fermentation bucket lids.
The snap-on cap has tiny CO2 escape holes drilled into it. The cap is easy to remove, allowing access to the inner “floater” cap, which is also easy to remove. The entire assembly is easy to take apart and clean. Use a tiny brush such as a dip tube brush to make it even easier.