This accessory works as intended, but there are a few things that bother me. First, the wall of the drill is thicker than that of a high quality drill of the same type. All of this means it takes a little longer to make a hole because more material is removed. Second, after reading the reviews, I realized that the set screw could come loose. This is a weak statement, one of my students lost it in a log wall a few minutes after using it. I bought a replacement from Menards for less than a few dollars. The only reason I bought this was because I couldn't order a core bit from our store on Thursday for delivery on Friday to drill holes on Monday at 6am. I ordered this on Saturday and it was delivered on Sunday so I could drill holes in the log wall behind on Monday morning during the planned slab. Use the red sealant on the set screw and leave it in the mandrel until you have tossed the entire assembly in the bin.