Abstract: The hole saw guide adaptor is a special adaptor for a standard hole saw which allows an individual to enlarge an opening in a wood or other work surface after an opening has already been cut in the surface. This adaptor allows an individual to increase the diameter of an existing hole that was cut with a hole saw. The adaptor would generally have a cylindrical configuration with a flattened portion on one end that allows it to be inserted into the hole saw arbor and locked into place with the set screw. The other end of the adaptor would include a threaded area similar to that on the lower end of any standard hole saw arbor. Thus, the hole saw used to cut the initial hole can be threaded onto this end of the adaptor, with the cutting edge facing away from the opening, to be used as a guide for cutting the new hole. The hole saw with the larger diameter for the new hole would be mounted in a conventional manner in the hole saw arbor.