The 3/8" Drive 3/8" F x 1/4" M Adapter with FOUR FLATâ„¢ Sides is designed from the ground up to be part of the most versatile socket family. Milwaukeeâ„¢ adapters feature an innovative design with four parallel flat sides, which deter rolling and are wrench-compatible. The drive sizes are laser etched onto the adapter providing improved, easy-to-read visibility. Chrome plating offers corrosion and rust protection. All Milwaukee Mechanics Hand Tools are backed by a lifetime guarantee.