Description must be wrong or something. The downstem isn't diffused at all. It's just solid glass, no holes or slits like mentioned in the description. Also the bowl isn't 18mm. It's a 14mm bowl. I tried putting an 18mm bowl in but it's obviously way to big to fit. Way too expensive and the 18mm bowl I purchased for it separately doesn't even fit. My first and last Roor. Price is insane for this old school bong that maybe should be in a museum instead of in-use. Tried a water test and my honeycomb hemper rig pulls better and smoother than this thing. Worst $330 I've ever spent. Not to mention the ash catcher I purchased for it doesn't fit either and that ashcatcher came scratched. I really hope I can maybe "salvage" this thing and get some use out of by purchasing a good Roor downstem for it. Not even sure I'll shop at DankStop anymore after this fiasco.