• High-performance alloy steel • Square female size: 30 mm, 31 mm, 34 mm • Hexagon female size: 3/8" • Phosphate finish • To be used with machines • For maximum safety use clamping springs • For bits with 1/4", 5/16", 11 mm male hexagon drive • 11 mm size is out of standards DIN 3126-C, ISO 1173 • Drive standard: DIN 3121-F 10, ISO 1174 • Standards: DIN 3126-C, ISO 1173