They work with Electric cone winders. There are mages showing the notch and the purpose of the notch. One is of a close-up of putting the pigtail in
Yarn Winders — CSM Love
Choosing the Best Yarn Winder and Yarn Swift – Fillory Yarn
National Artcraft® Heavyweight 7 Cardboard Fiber Cone - Perfect for Angels, Dolls or Tree Toppers (Pkg/60)
Keep your yard clean and organized with these empty cardboard yarn cones from The Woolery! These cardboard thread cones come in packs of 25, 50, and
Cardboard Yarn Cones
Cyllde eew Cone Winder Yarn Winder Hand Operated Portable Corrosion Resistant Plastic Wool Winder with Detachable Winder Head Swift Yarn Winder needlecraft Yarn Ball Winder
yarn cone winder
Cardboard Craft Cones FOR SALE! - PicClick
Winding yarn on a cardboard core
Cardboard Cone
Cardboard Cones for Crafts, Winding Yarn, Lot of 4, Works with Cone Winders