FUNCTION: This socket adapter is specially designed and used for manual drive applications or with power tools when used with plug-in shanks. MATERIAL: This socket adapter is made of hardened and treated HSS, which has great strength and endurance for long time use. SIZE: Square Tip Size: 10mm / 3/8"; Hex Shank Size (Approx.): 6.3mm / 1/4" SPECIAL DESIGN: This socket adapter has a very special design part of spring-loaded ball bearing on each square head, in order to effectively fix the socket and avoid sliding. DOUBLE SIZE CONVERSION: The original hexagonal polygon size is converted to a square head size, which can be used to mount the sleeve as a good accessory for conversion.