These upstems are made for the Stündenglass Gravity Infuser. They're made of aircraft-grade aluminum and are easy to install.  They're official Stündenglass replacement parts and they're easy to use and install. 

The Stündenglas upstem comes in two sizes: Small and Large. The small upstem is for the Stündenglass Small Globes Kit and the Stündenglass Kompact. The large upstem fits the original Stündenglass Gravity Infuser.. 

These diffuser upstems are a key part to the Stündenglass functionality. As you rotate the bong on its axis, the  upstems are responsible for filtering your smoke through water so you can enjoy smooth and tasty draws.