Add a tassel to a graduation cap by tying a slipknot around the tassel and the button on the top of the graduation cap. Use fishing line to make it as unobtrusive as possible. Otherwise, use a single thread that is the same color as the graduation cap. Add several tassels for a unique and fun look.
Use yard to attach a tassel to a child's version of a graduation cap. If the cap has a button, wind the yard around the button several times, then tie it to the tassel for strength. If it won't wind, punch a hole into the cap using a hole punch and tie the tassel through the hole.
Stitch a tassel to a hat using fishing line to secure it tightly and permanently. You can attach it at the center of the top, or on either side near the ears.
Secure a button to your hat and use the loop at the top of the tassel to secure it to the button. This method will allow you to change the tassels at will, or to use more than one at a time for a fun and unusual look.