|Source Mod||Buildcraft 3|
For example, iron pipes have one output port and many input ports. In order to change which port is the output, you need a Wrench. The output is indicated by the port that does not have a little gray rectangle on it.
Wrenches are also very helpful when you discover that you placed something the wrong way. Each time the wrench is used the target engine/pipe will cycle through valid orientations. This means for example wooden conductive pipes have to be placed before attempting to rotate an engine or it will not move.