Pencil lead works for a moderately tight stem. I have also used the Burt's Bees Lip Balm for both tight and loose stems as the #1 ingredient is beeswax and is available at any drugstore. Another great use for the lip balm, and my favorite, is treating your vulcanite stems. Immediately after a smoke, I wipe off any gunk with an old washcloth and dry it, then put just a little dab of lip balm onto the stem and rub it around with my finger, taking care to get the button indentation real good. Most times, I just put it back on the rack and let the balm soak into the pores of the vulcanite. Then if needed, wipe off the next time you smoke it but normally that isn't even necessary as it has been absorbed. You will greatly reduce stems from oxidizing and it only takes 5-10 seconds after each smoke.