You need these for blocks on a DC system and for turnouts on DCC systems. These work on the HO and the HOn3 track system by Shinohara. A big plus is that they are not orange - like another manufacturers insulated rail joiners. For years, Shinohara was considered the top-grade trackage system. Now there are some serious competitors and I am experimenting with several track manufactures to find out which one is the best.