This 21-piece metric crowfoot wrench set is designed for fastening and repair work in tight spaces. It is forged from 40Cr alloy steel with 38-45 HRC hardness for strength and durability. A black phosphate finish helps resist rust and wear, while the 5-point contact design helps reduce slipping and rounding. Dual size markings on both the tools and storage tray make identification and organization easy. It is compatible with ratchets, extension bars, and torque wrenches for automotive, plumbing, maintenance, and DIY use.