Quality: The double ring wrench set is made of premium chrome vanadium steel with mirror polished finish. Chrome plated for rust resistance, heat treated for maximum strength and drop forged for long life. S-Type Key: S-shaped keys with curved design are perfect for easy access maximum in confined areas, such as assembly or disassembly of parts in an automobile engine or in machinery, making your work easier. 12-point box end: the end of the 12-point box of the double box wrench set is designed to grip the flat sides of the fastener heads, to prevent rounding and increase the contact area and locking groove, easy application on the fastener. 5 pieces: This Type S obstacle wrench set includes sizes: 10x11mm, 12x13mm, 14x15mm, 16x17mm, 18x19mm. And two sizes per wrench provide more options with less transportation. Wrench sizes are stamped on both sides of the handle for easier size identification.