The wood saw on Victorinox Swiss Army knives is about 2 7/8" (72mm) long. It is extremely sharp, and cuts on both the pull stroke and the push stroke.
You can use the wood saw to cut wider pieces of firewood by making two cuts in a "v" shape, working all around the outside until it is narrow enough to snap.
WARNING: Use light pressure when sawing, and be careful that the saw doesn't bind, since it can bend at the base and eventually snap off, if pushed with too much force.