I am a specimen carp angler. the rubber tubes are called anti tangle sleeves. it is used for the exact reason rudolph says that it stops the line from coming back onto itself and tangling around sinker, hook and main lines. Just one thing we usually do is not put supaglue but rather slip it over the first ring of the swivel( the ring you attach the line onto) that way you avoid the slipping and its just gives it more security and a better chance for the anti tangle sleeve to work better. just a note the sleeves can be bought separately on its own and in larger qtys thereby saving money.