Gut string, gold/silver wound, knot end. STIFF version, available in the gauges:  

Steelstring, gold plated, ball or loop, medium, light and heavy.

Gut string, gold/aluminium wound, knot end, available in the gauges: 

Gut string, gold/aluminium wound, knot end, STIFF version.

Gut string, silver/gold wound, knot end, available in the gauges: 

Gut string, aluminium wound, available in the gauges: