These bits were the best I have found so far. If I find a stronger one, I'll let you know. Don't hold your breath, I don't think I'll find it! They've all found that they end up lasting a lot longer than anything I've bought in years. I'm notoriously bad with tools, especially end mills and the like. I found them particularly hard when cutting stainless steel. That's why I bought them. You have held up well. It's always hard when they break, no matter when. Whether they lasted many hours or…