Stays made from puddled iron bar were used as a cheaper alternative to copper for joining the inner and outer firebox plates of steam locomotives. The incorporated stringers gave flexibility akin to stranded wire rope and  stays made of the material were therefore resistant to snapping in service. Wrought iron rivets made from iron bar typically contained stringer filaments running the length of the rivet, but filaments at right angles to the tension, particularly beneath the head, caused weakness.