A four year old thread revived!

Yes, One has a 55 degree cut angle and the other is 60 degrees. I forget which way round it is. As you say, if you put the screw of one into the thread of another there will not be a flat to flat surface bearing the force. It will work but will wear with continued use.

The original difference of opinion here was with which thread was used. I claimed Whitworth but others (usually Americans) thought it was UNC. The fact that many cameras were made with 1/4" x 20 tpi threads before UNC was unified makes me think that it was originally Whitworth.