Wheel

The wheel consists of three same-coloured pieces around a central point.

The red pieces are strongly connected to each other. Blue cannot break the connection between them, and his available forcing moves are not very good. It also has a big circumference, so that it is easy to connect to it from other parts of the board. The drawback is that it requires three pieces and is rather compact, so that it is often not efficient enough.

Blue has three possible forcing moves, labelled A. If Blue plays in one of them, Red can restore the connection by playing in any of the other cells labelled A. (He can also play at B, but it's usually not so good.) By doing this, Red strengthens his connection, and the influence his pieces has on the rest of the board. It is therefore usually better for Blue not to invade.

Blue should never attempt to invade by playing at B. Red can then restore the connection between his pieces by playing at any A. Red's position improves, while Blue's piece is useless.

U-turn

Note that the position below, where Blue has already intruded into one of the starred cells, is a very weak one. In this case, Blue should play at the midpoint, which is now the point where two bridges overlap.