My few experiences with machined Chinese product I have come to the conclusion they really DONT know how to do it!
I'm sure your fastener should be 6x1. I bet you can almost turn the tap in by hand. Just turn it in a little at a time and make sure it goes in straight.
Not a hard job. 6x1 is the only tap size I have worn out multiple times. Keeping one around will save you headaches later.