Its RG6, electrically very similar to the CT100 you might use for televison use, it can be jointed with an 'F' barrel connector if termined into 'F' plugs, or split with a suitable splitter
All work on NTL's network should be carried out by their own teams though, read your contract of service
, they won't be happy if you start connecting so called 'low loss coax' from
wickes into it...