A LITLE METAL PIECE THAT YOU PUT IN THE END OF THE COAXIAL CABLE

LIKE THIS....WITHOUT THE CABLE....AT THE END OF THIS YOU HAVE METAL!!!

IT CAN BE VERY SMALL AND ALSO LOOKS LIKE A METAL RING....WITH A METAL END...LIKE A EARING!
http://www.redcoon.pt/index.php/cmd/shop/a/ProductMainList/cid/9000/Cabos_de_audio_video/