Rubber rings for attaching lights etc I have some lights and a cycle computer that attach using some sort of rubber or silicone bands (or O rings - don't know what they are called). I need some replacements, but I don't know what they are called!

Best I can find on (say) Amazon are O rings that look the same but seem to be only for plumbing - not long term daily use on a bicycle.

I need various sizes as I want to move stuff between bikes - which have differing tube/handle bar diameters.

The technically right name - or a recommended supplier - would be most welcome!
Have you thought about cutting an old inner tube across its length. Various thicknesses of cut give more or less stretch. Rubber versus latex, too many different size tubes to mention. Cheap as chips and your LBS will have an endless supply.