From the product description, check product page for current description, price and availability:

Our mini and medium 2-piece airlocks are a great option when a single inch could make or break fitting your carboy into a fermentation chamber. The airlock breaks down into 2-pieces for easy cleaning. Instead of a floating center piece, like standard 3-piece airlocks, the center piece is molded into the lid. One less piece to clean and misplace!

Another cool feature of this 2-piece airlock is that 1/2″ ID tubing will fit onto the center post for use as a blowoff. This can be handy if you have a really active ferment that is blowing out the top of your fermenter.

• Holds approximately 0.4 fl oz (12 ml)
• Chamber – 1-1/2″ tall x 1-3/8″ diameter
• Stem – 1″ long
• Stopper not included