ESCO CAST SCREWY DRUMLINE FERRULES Screwy drumline ferrules incorporate the cast Screwy design in a shorter ferrule, designed specifically for attaching winch lines to winch drum pockets. Note: Drumline ferrules develop less holding power than choker ferrules and should only be used to attach wire rope to winch drums. Never load drumline ferrules directly. Always leave at least three wraps on the drum when it's under a load.