I fill the donut bobbin holders with bobbins full of different color threads to put on my guild sale table. It's great to have so many color selections in one place when handsewing. I buy the metal bobbins at Wal Mart. I have lots of thread that I know I'll never use up so I wind bobbins. It's all cotton or all poly I don't mix the bobbins in the donuts. Each donut will hold 30 -35 bobbins. It's a great way to use up all the extra thread spools.