I have a business that provides low voltage installation services. If you dull the bit, you'll have to replace the entire bit ($30-$50 each), not to mention you'll end up needing 4-8 different bits for different bit sizes and lengths. It is easy to attach a new bit and the edge design prevents the bit from spinning freely. The reason for the 4 stars is that you really have to make sure the screws are tight or you'll get stuck in the wall. FYI, 90 degrees for the entire length of the rod, don't…