I wanted to create the threading on an external part by inserting the internal part with completed threading into the external part and then doing a subtract combine.  I've been trying to figure out how to get this to work when reliefs and chamfers are involved and I keep running into problems, and I'm not sure how to resolve it.  Attached is the external threading part which is the main body in the combination, with the inserted internal threading part which is the body to combine.

When I do the subtraction the error appears: The feature could not be completed (failed to merge bodies).  Any tips? I can get it to work properly as long as the internal threading is not subtracting from the external chamfer, but I want the threading to cut into the chamfer as well.

If all else fails, could someone take a look at the threading I am currently making separately on the external part, and help me make sure it will thread the internal part properly?

Thank you!