The 4 holes for the mandrel pins were slightly offset and the mandrel would not engage in the holes. I would have returned this hole saw for that reason, but I needed to get the job done so I had to enlarge the pin holes a bit so the pins would snap in order for me to be able to use the hole saw. Another problem is that the internal depth of this hole saw is exactly 1-1/2 inches, so you can barely cut through a nominal 1-1/2 inch thick joist. Other hole saws from Lenox or Milwaukee are slightly deeper so they can easily cut through the joist. Finally, this hole saw is 210mm or 8-5/16" in diameter, not 8-1/4" as advertised.