I read somewhere in the ether that you can make your own bits from vinyl tubing bought at your local hardware store for pennies a piece. I tried it and am very happy with the results thus far. I bought a 10ft roll of 3/8 outside diameter tubing in the plumbing section of the hardware store for less than $5. It is marked non toxic, bpa free, etc.. I cut it into 1/2-3/4 inch pieces. Slip a small pair of needle nosed pliers inside of it the dipped it into boiling water for 30 second. Force open the pilers and put it over the stem, then remove the plyers. It was a little loose, so back into the boiling water for another 20-30 seconds and it formed quite nicely to the stem. Not even my snaggletooth will puncture it. I call it a win!