Answer:
This thing all things devours: Birds, beasts, trees, flowers; Gnaws iron, bites steel; Grinds hard stones to meal; Slays king, ruins town, And beats high mountains down.
What has to be broken before it can be used?
Three little letters, a paradox to some. The worse that it is, the better it becomes.
I'm not really more than holes tied to more holes. I'm strong as good steel, though not as stiff as a pole.
In buckles or lace, they help set the pace. The farther you go, the thinner they grow.
Those with eyes bigger than their stomach will definitely leave the restaurant with one of them. It is named after a house pet as well.