I use commercial weed-whacker string. It's about 1/4" dia. and very loud and stretchy. I've tried leather, sisal and cord with poorer results. Be sure you buy round w-w string, some is square and grooved and will destroy gloves not to mention hands. It's good to see Cap't Bob here again! I built a trash can bass from Dennis Havlena plans too and it's incredibly easy to control. Try it, you'll like it! How's it goin' Cap't?