Assuming you have a typical dial caliper, measure the ID of the screw hole. It will likely be near a fraction minus the thread depth times two. We can probably guesstimate a good fit of a standard bolt from this measurement. You may want/need to run a modern tap through the hole to make sure the new bolt fits reasonably. This is not the most technically "pure" repair, but a very practical one. Post the diameter and we will begin the rumination.

DDA