Yep, the case hardware screws won't work perfectly with the Mouser part. I would personally recommend to use the 4-40 MF standoffs that come with the DB-25 socket as case mounts and keep the black screws for another day. Then you can properly mate a DB-25 cable. If you prefer the look of the >>panhead<< screws, feel free to mangle the thread in the DB-25, but you need nuts on the inside to keep it tight.