I picked up a mobile at a garage sale. In the process of untangling the lines and cleaning it up for my grandkids, I discovered that the knots at the ends of the threads keep coming undone. I think it's because the line is very slick. It's much thicker than thread, but thinner than most string. It's about the thickness of fishing line, but made of something that looks like nylon.
In any case, it won't stay tied. Where the other end of the line is tied to the crossbars, it looks like they used some sort of glue. The line is very hard and rigid. Those knots do not come untied.
Can I buy something that will cement the knots so they can't come untied?