Material: Chrome vanadium steel The surface is electroplated and blackened, and the corrosion resistance is good The adapter body is designed with a changeable square head size to fit your more sizes There are 4 plug adapters of different sizes in this set Small size, easy to store This is a set of 4 plug adapters of durable gear reducer and gear increaser. Heavy-duty chrome vanadium steel construction is designed for use with ratchets. The black oxide finish makes each piece corrosion resistant and very durable. Spring-loaded ball stops keep your sockets secure. Available in a variety of sizes for multiple socket or wrench combinations, including 1/2'(M)--3/8'(F), 3/8'(M)--1/4'(F) , 3/ 8'(M)--1/2'(F) and 1/4'(M)--3/8'(F). Specifications: - Material: Chrome Vanadium Steel - Surface Treatment: Electroplating, Blackening - Hardness: 45±2 (HRC) -Color: Black Package Contents: 1 adapter 4 pieces