Oh boy. That is not good news.
I'll let someone else elaborate on that.
The interrupted thread is interesting. Don't see those very often. This 'style' of barrel has been discussed here several times, with different opinions as to what threads on the barrel.
You could likely find a machinist who can make you a replica of a Luger front sight band & blade to thread on your barrel, but it might be easier & cheaper to just buy another barrel and have it installed.
What did the seller tell you the threaded muzzle was for???
