Replacement Showerhead Downstems are a good upgrade or replacement glass bong downstem for any type of water pipe. These glass downstems add a high-functioning percolator improving the hit of your glass piece. Alex K downstems fit most standard bongs, bubblers, and water pipes requiring an 18/18mm fitting. The 18/18mm showerhead downstems feature quality boro glass and several diffusion slits for added airflow and superior water filtration. Alex K replacement downstems are handblown in Arizona from a quality, American borosilicate glass.