means they probably need tape (i.e. rims which it is possible to set up tubeless with the correct tape, valves, tyres, etc.).
Some people … put a wrap of electrical tape round first so that you can pull the gorilla tape off without leaving a gunky mess on the rim.
I leave the normal rim tape in position which would achieve the same result, but the waterproof duct tape that I’m using currently doesn’t leave much of a residue.
If the rims are less than roughly 21 mm wide, then the 25mm tape will probably be OK. Any wider, and you’ll probably need wider (50mm) tape and slit the roll down (or put several wraps of narrower tape on, as above, but I prefer keep the ways that the sealant can get under the tape to a minimum – YMMV).
I try and get the width of the tape such that when it’s stretched tightly into the rim bed, there’s just enough to turn up at the side of the rim (only a mm, or less) – that way, the tyre bead can seal directly on the tape and also hold the tape down.
It doesn’t have to be Gorilla tape. Clear waterproof tape works, as does waterproof duct tape (which is what I’ve used most recently).