I used S-20-05-N
disc magnets to attach a belt to my ukulele.
This way, I didn't have to drill and antique instruments keep their original condition.
I just used double-sided adhesive tape to glue a magnet on the inside of the ukulele, and I sewed another magnet into the red belt.
Then I carefully brought the end of the belt up to the ukulele.
It works great!