The little arc-shaped piece that is printed next to one of the halves of the reusable spool. After you put the two halves together, you have to shove that piece into a slot inside the spool, to lock the two halves together.
The little arc-shaped piece that is printed next to one of the halves of the reusable spool. After you put the two halves together, you have to shove that piece into a slot inside the spool, to lock the two halves together.