Ok, so these nitrile rubber bands.....

[Caprimulgus]

I have seen modular column sections sealed together on the outside with seemingly black rubber bands. "Nitrile rubber bands" have been mentioned. And searched for them......nada! Is there a nother word for them? Or, are they simply made at home out of something ells? Like cut up bicycle tubes, or something? Oh great guru's, tell me your secret!