Thanks. I'll check on that. BTW, I received an answer from Charge (though they may be not be referring to the threaded dropouts):

Q: "Hello. I recently purchased a 2015 Charge Plug (Performance Exclusive). On a bike discussion forum I read that if I were to add a rack to the back of the bike, I would need a particular set of screws. Could you tell me what type/thread I should look for when I go to my neighborhood hardware store? Thank you."

A: "Hi...These should be a normal M5 bolt, the same as the bottle bosses. I’d take a bottle bolt out, thread it into the rear and if it works, buy a matching set. The bolts that come with mudguard sets will work, it certainly did in mine."

Kind regards,
Charge Bikes"