Good Luck saw chain for a chainsaw: 76 links, 325 pitch, with the marking 45-20'' given in the name. The chain cuts wood with its teeth, is driven by the sprocket, and is guided along the bar.
The chain needs to be replaced when the teeth have become dull and can no longer be sharpened, the saw pulls to one side, produces fine dust instead of chips, or the chain has stretched and constantly sags. When choosing, the number of links and the pitch must match the previous chain, and must also fit the sprocket and bar of your saw.
