This Sunex 3/8 inch drive impact universal joint is made of CR-MO alloy steel for long life and is fully guaranteed. Forged from the finest chrome molybdenum alloy steel – the best choice for strength and durability with a radius corner design, to extend the life of fasteners. The design drives the side of the fastener instead of the corner which provides increased strength, but also avoids rounding of rusted or damaged fasteners.