I was hanging a ceiling fan in this room when I discovered that the mounting screw holes in the electrical box are stripped. My dad has suggested using JB Weld putty, letting it cure, drilling it out with a small bit and then using wood screws. I’m a first time homeowner and have neither the confidence nor the expertise to completely replace the box. Is my dad’s route the best course of action or is it a waste of time and/or dangerous to go that route? Thank you!
Definitely don’t use JB weld, and I think you should be able to do it without replacing the box.
Regular electrical boxes are usually 6-32 size screws, ceiling fan boxes usually 8-32. If the holes are stripped, especially with plastic boxes, a lot of times you can get away with using the next size up (either 8-32 or 10-32) and forcibly screwing them in. They will cut new threads in the soft plastic/metal of the box, and you’ll be good to go. This is how most electricians would handle it without replacing the box.
If you want to do a cleaner, less hacky job, you can get a set of drill-taps, like this:
https://www.homedepot.com/p/Klein-Tools-Drill-Tap-Tool-Set-4-Piece-32383SEN/304401087
Or the hand tool: https://a.co/d/6fr9d4Z
You can usually find them in the electrical section of your big-box home improvement store of choice. Just use the next size up and get some appropriate screws.
I will second getting the Klein tap set and just drilling and tapping the hole and using a size up. Replacing the box is by far the best thing to do, but tapping the existing box is fine for the next 10 years.