Silky Zubat blades are impulse hardened on the tops of the teeth. This flash heating places a hardened case around the tip of the tooth that keeps the teeth sharp for longer. The time length is equivalent to three sharpens of a non impulse hardened blade. For the average home gardener a blade will stay sharp for many years. For arborists and orchardists using their Zubat on a daily basis, the average replacement time is a year.