Abstract: A headed steel pin for a multi-grip fastener of the pin and swageable collar type has a homogeneous microstructure, and consists substantially entirely of sorbitic tempered martensite. Suitable coarse-grained medium carbon steel is shaped to form a headed pin having a plurality of identical, regularly spaced, annular, combination grooves each able to function alternatively as a locking groove, a pulling groove, or a breaker groove. The shaped pin is heat treated, the steel rendered homogeneously martensitic and then tempered at a temperature approaching as closely as practicable to the lower critical temperature of the steel, to convert the martensitic steel entirely to sorbite. The finished pin has a suitable balance of brittleness, toughness, ductility and impact strength, and tends to break cleanly and reliably at a selected one of the combination grooves when the fastener is installed in a workpiece.