While you can have different lengths of cord in each hole, to achieve better balance we recommend the same length of cord in each space on the varying arms. For example, if you use a five-inch piece of cord in the hole closest to the center, a seven-inch piece of cord in the center hole and a nine-inch piece of cord on the outside hole, repeat that pattern throughout the mobile.
After you've secured all the strings, begin tying the bats to the ends. Again, use a small double knot to secure them in place and singe the ends.
Secure all the bats to their corresponding strings and you're all set!