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
Cardboard Cones for Crafts, Winding Yarn, Lot of 4, Works with Cone Winders
Why does yarn tangle in the middle of the skein? - Quora
Royal Cone Winder Cones
Cardboard Cones
Wide bottom, narrow top. Cone is 6 3/4 high with a 2 5/8 diameter base. For use with the Silver Needles Cone Winder or any winder that accepts this
Cardboard Cones - Erlbacher Knitting Machines
Other Needlecraft Supplies, Needlecrafts & Yarn, Crafts - PicClick
Cardboard cones lot of 10 pcs, yarn cones for winding, thick paperboard cones, craft cones, paper mache cone, tree shape
Atlas Insider: The Long and Winding Road – Modern Daily Knitting
National Artcraft® Heavyweight 7 Cardboard Fiber Cone - Perfect for Angels, Dolls or Tree Toppers (Pkg/60)
Needles to say: 2016
CARDBOARD CONES FOR Crafts, Winding Yarn, Lot of 25, Works with Cone Winders $16.50 - PicClick
Cardboard Craft Cones FOR SALE! - PicClick