Just wondering the string doesnt fit all the through, so it doesn't completely clear the nut at the top.........file it down? If so, what's best to use? If not, what are my options (other than get different strings)
Don't start filing on the strings, you'll break a wind and probably shorten the life of the string. I would discretely alter the bass so the string will fit. I've had to open the holes on most of my basses to accomodate larger strings. As long as there's still a neck for the ball end to hold onto and not pass straight through, you'll be ok.
You can file that channel up to 3/16" wide and still have the ball end hold. I have actualy drilled through ferrules and bridge plates to accommodate a .185 without issue.
If it were mine to do I'd widen the slot in that tail piece.
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