The No. 226 ³/₁₆” adaptor adapts our No. 224 ³/₁₆” Solid Carbide Drill Bits to work in a standard electric drill chuck. The shank diameter on the adaptor is ¹/₄ inch. An internal collet tightens down on the drill bit to hold it in the adaptor. Made from steel, heat treated for wear resistance, and zinc plated.