Wheel

The wheel is a 3-stone interior template. It consists of three same-coloured pieces around a central point, along with the four empty cells marked "A" and "B".

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. The wheel also has a large 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 to cover a large area.

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. (She can also play at B, but it's usually not as good.) By doing this, Red strengthens her connection, and the influence her pieces have on the rest of the board. It is therefore usually better for Blue not to intrude.

Blue should not usually attempt to intrude by playing at B. Red can then restore the connection between her pieces by playing at any A. Red's position improves, while Blue's piece is not very useful. Although Blue still has to opportunity to intrude in one of the remaining cells marked A, it would have been better for Blue to do this in the first place.

U-turn

The wheel should never be confused with the U-turn, shown here:

If only two of the cells marked "A" are empty, and not all three of them, it is not a wheel and it is not a template. The U-turn is a very weak position. The U-turn sometimes arises when a player tries to connect via bridges and takes a sharp turn. The problem is that Blue can play at B, leaving Red unable to defend both bridges.

The intrusion at B

While in most cases, it is not a good idea to intrude into the wheel at "B", there are some positions where a move at "B" is winning and all of the moves at "A" are losing. Such positions are quite rare. Here is an example, with Blue to move.

Note that "B" is the only winning move inside the wheel. However, there is also another winning move for Blue outside the wheel, at "*".