These arrived earlier than planned which was a nice surprise so I will be able to give them for Christmas. After trying them out I decided to swap out the fine yarn for som micro chenille that I had in my fly tying kit and now they work even better. The trick is figuring out how to tie the yarn/chenille into a loop without too much of a knot or a bump that will hinder the wheels. By using a fly tying bobbin and some fine thread I was able to make a fine connection with a small dab of crazy glue to seal it. It’s quite a surprise to see just how far the loop extends when it’s running. It’s a magical little gizmo !I purchased this product from another seller. The string broke after 10 seconds of use. You can not replace the string because the knot won’t go through the toy. I requested a refund and noticed that Amazon already took the Seller down. This is a scam. Do NOT buy this product.