We recommend the 21mm yellow tape for the Alpine and Alpha 340 rims, as well as any other narrow rims (under 23mm external width). It will also fit wider rims, but it's better for the tape to come very slightly up the sidewalls of the rim to avoid it being lifted by the tyre bead and allowing air and liquid to get under the tape. For the Crest rims, NoTubes recommend either the 21 or 25mm tape; we say go with the 25mm, it seals the rim better and more reliably. All other NoTubes rims (Podium, Arch, Flow) always use 25mm tape.
This is how we fit the yellow tapes at JRA:
When fitting the yellow tape, rub the inside of the rim thoroughly with medium wet & dry to take off ridges and burrs around the spoke holes and the other small holes around the rim. Clean the rim thoroughly with degreaser and start applying the tape opposite the valve.
Begin by pressing down a short section (about 50-70mm) so it's stuck firmly across the rim. Then hold the wheel between your feet and apply about 25cm of tape at a time. Pull the tape as tightly as you can while pressing it down onto the rim. The tape should go on in a smooth manner, with no bubbles or wrinkles. You might need to use a side-to-side waggling motion to get the tape to form to the rim properly. Always maintain very high tension on the tape - literally as hard as you can pull.
Overlap the ends of the tape about 70-100mm and cut with scissors. Cut a small hole in the tape for the valve and make it exactly the size of the rim, either by trimming with a very sharp scalpel or using light downward strokes of a small round file. Press down the tape to make sure it's well stuck down all the way round, including around the sidewall area.
Fit your valve or rimstrip, and the tyre and sealant, and inflate.