These bits have been on my hammer drill more than a few times and both have punched smaller diameter holes though concrete, brick & granite with relative ease. The bits appear tough, they're still sharp. Out of the box they looked like quality percussion bits, with well machined flutes and clean, sharp carbide tips compared to a sloppy, $14.00 Vermont American set I own:http://www.amazon.com/Vermont-American-1402199-Double-Masonry/product-reviews/B003O9AAW2/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints;=1This set comes with two 1/4" bits as it's a very common sized fastener gauge. The larger bits have three flattened areas on the shank to insure a solid gripping surface to prevent slipping in the chuck on a bind. These bits are not just "disposable bits" like other, cheaper ones on the market.