I've broken many wooden handles, but have yet to break a fiberglass one. Bent it, yes, but it always snaps right back. Now, the Kobold (sp?) brand from Lowes has a life-time guarantee and I've broken 3 from them.. but always the blade & never the handles! I can't see how you'd break the handle on a fiberglass.. and I have dug out many stumps with my shovels.
