I'm "tuning up" a "department store" Schwinn with a 7-speed rear derailleur. After adjusting the brakes, truing the wheels, etc. I took it for a short ride. I noticed it wouldn't drop into the lowest cog, so I tried adjusting the rear derailleur. With the low-gear limit screw all the way out, it still wouldn't go into low. That's when I noticed that the rear hanger was slightly bent. I removed the derailleur hanger bolt and clamped a crescent wrench on the hanger and "persuaded" it back into position - it didn't need much - but now the bolt won't thread back in. I think I need to chase the threads.

I'm wondering if anyone knows the tap size?