I have been using just a simple "steel" file, I may have to look into a little better quality one because after about 5 stems my file is very dull. I got my stems from Gotvape.com. they had them on sale for $1.00 each so I picked up a bunch. They are long bent stems so in order to use them like a "stock" stem I had to cut them. Here is how I cut down my Vapolution stems. These were my starting products First I find my ideal length for my stem and mark it with masking tape. Then using my file I make a light "scratch" all the way around the stem. After I have my mark I can remove my tape and really go at it with the file. Sometimes, while I'm filing the stem, it will break on it's own along the crack once I get a good deep groove. Other times like today it ain't happening, so I must break it. I simply wrap it in a rag and break it by hand. It takes very little pressure. If you end up with a "jagged" edge simply clean it up with the file or sand paper. I just bit the pieces off with pliers. Now that the hard part is over, a nice little flame polish and were almost good to go. After a good cleaning you should have a nice finished glass stem. Now just add your preferred washers and fill with your preferred herb and enjoy. And not that I have to tell any of you but the extraction of this thing is second to none. Again Thank you to @lazylathe for being a real pioneer and thinking outside the box with these stems.