What pipe is this?

[imy2k]

Hi all, one of my pipes what goes into the radiators has ripped off and i need get a second hand one or new one. What is it called? Thanks in advance

http://i1307.photobucket.com/albums/s588/imy2k/null_zps98634bb5.jpg

http://i1307.photobucket.com/albums/s588/imy2k/null_zps9b9975ca.jpg