These are very good masonry drill bits but cannot be used with hammer drills so work slowly. It takes 2 to 5 times longer to drill a hole compared to a comparable hammer drill (on a hammer drill). With the smaller bits this isn't much of a problem, but the 12mm bit took so long to make the hole that I gave up and ended up using the hammer drill. Using a hammer drill (following the instructions) will make the process much faster, but not as good as a hammer drill. seemed to work fine.