14-18mm and some super small pieces for smaller glass. Works with all my glass, currently 6 bongs and around 10 bowls and 6 ash catchers. makes it possible to shake the bong like a maniac . my glass get super clean super fast now. I use cold water from the backyard hose to rinse all the pieces out. will buy more when needed .

I had to shave a small amount from the large plug so it wouldn't pop off. The other plugs worked well.

I only wish that there had been 4 sizes. The large one is not large enough to plug up a regular old bong. Which I have and still use. I like the new things that I buy at 420 Science, however I do switch off while other Pipes are awaiting to be cleaned. There are 3 plugs. There were really two sizes I needed. 1 smaller to fit my new pipe and a larger one. But, what are you going to do. Just wait until something else comes out.