The Tunnel Single and Double Deadends group of Naked Geomorphs contains 15 tiles, each with one or two unconnected tunnel entrances (T), and rock (R) at the remaining four or five positions. There are actually twelve different connection patterns; this group contains two tiles for each single deadend pattern, because those are so useful as edge and corner tiles. Sets A and B are completely interchangeable. I.e., tile T165B can be replaced with tile T165A, without changing the basic structure of your map. Set B has broader tunnels than set A, with no one-hex-wide constrictions in the main passages.