Corrosion resistance: The surface of each adapter is electroplated and blackened to ensure corrosion resistance. Durability: The socket adapter is made of heavy-duty chrome vanadium steel, which has durability and long lifespan. Design: The adapter body is designed with a spring ball pawl and a small hole to maintain the stability and safety of the socket. Multiple options: There are four different sizes of socket adapters that you can use for different sockets. Note: Common size combinations result in a doubling of the range and capacity of many sockets. Features: Surface treatment: electroplating, blackening Quantity: 4 pieces size 3/8 "(square hole) -1/4" (square head) 3/8 "(square hole) -1/2" (square head) Package includes: 4 x sleeve reducer