Hole saws have been around for decades and the same problem has existed since day one - the plug gets stuck inside and renders the thing useless. Well say goodbye to that problem. This new style of hole saws has an arbor that allows you to push out the plug if it gets stuck. The hole saws have carbide tipped teeth for drilling in tough materials like fiber cement board (i.e. HardiePlank™), gluey MDF, wall tiles and plastics as well as wood. The threads on a standard hole saw arbor are universal and could be used with an extra long pilot bit, but why would you want to when the Drill & Drop arbor ensures that you can remove the plug from the saw? If a plug gets stuck, simply depress the spring loaded, knurled lever on the arbor and pull the hole saw back to expose the plug for easy removal. To assemble the arbor to the saw, pull back on the spring loaded collar, spin the saw on the threads, line up the pins with the holes in the back of the saw and release the collar. Cutting depth is 2-1/4". Purchase arbors and extensions separately. Made in Holland.