** The most common size that fits a variety of applications is the 2½” x ¾” **

Shorter air blocks confine air mist lower in a reaction tube increasing contact time.
Longer air blocks will handle higher pressure air pumps for much larger applications. 

Limewood, also known as Basswood, is a light weight, strong, odorless, close grain hardwood that will not split easily. The low notable grain creates a high porosity, that produces an ultra fine froth of mini air bubbles making it ideal for aquarium applications like lift tubes and counter current protein skimmers.
A rigid stem is firmly pressed into and extending 3/8” from the block. This 3/16” diameter tube allows a firm, sealed connection of standard aquarium flexible vinyl or silicone airline tubing. This non-barbed tube allows the installation of an optional rigid centering stabilizer (not included). An air block centered within the reaction chamber promotes more effective effervescence 

Being firmly pressed, this non-bonded stem may be removed for alternate applications where a stem may not be required. This can be accomplished with a simple pull and twist using a pair of pliers.