I ordered a 12mm diamond crusted hole drill bit and it works like a charm for drilling holes in glass vases to make homemade bongs... My next project was to make my own glass diffuser downstems which I can put into the bongs I make and use with either a glass drop cone (just a simple glass cone with nothing attached, sits on top of the stem) or a glass slide cone (the kind with the grommets). The original idea for making my own diffused downstem was to cut slits in the side of a 12mm diameter test tube near the bottom... after investigating what a normal rotary tool cut-off wheel can do to glass (shit all - cuts so slow I haven't gotten through glass yet) I investigated a diamond cut-off wheel for making the slits... but alas I hear they leave a poor finish on glass and may not be suited to the job... I am at a loss here can someone please tell me the appropriate tool for making these slits? Preferably for a household drill. The new idea (not sure on this one yet) is that I might be able to get a diamond crusted etching tool and by holding it in the same place, cut holes in the bottom of the tube to make a more traditional diffuser with the round holes... any ideas if this will work? Or another method of making such small holes in glass so close together without cracking/smashing? TLDR: Basically to sum up this thread, I need help with the appropriate tool/bit to cut slits (or possibly very small holes, very close together) in the bottom end of a glass test tube to make a diffuser downstem for my homemade glass bongs. If anyone can please offer some help on the matter it would be much appreciated... I am currently at a standstill on my project... importing glass on glass or slide with grommet style stems and cones is an option but due to the cost it will only be an option for a small handful of the better pieces I make. I'll be sure to post pics when they're done, too! - I want to make multiple bongs for me and each of my friends and maybe even sell a few... Fighting the NZ glass bong crisis!