Major_Tom....
If you don't already have them...Harbor Freight has a set of Mini Files that can be used to clean up the threaded section that has been drilled through, also use a wire brush to get all the grit out. If you still find it difficult to the the threaded sections together use a little tooth paste on the threads and carefully work them back and forth and that will also clean them up, rinse and your ready to go. Sounds like you want these sections to act as a single piece so that simplifies it further. Gary