Diameter: 5/16"</br>Drilling in Hard and Abrasive Materials</br></br>Product Description</br></br>Bosch cobalt bits offer superior durability?? speed and selection for most metal drilling applications. Used for Heavy-Duty drilling in extremely hard or abrasive materials. Best used for drilling into light gauge metal?? high carbon steel?? aluminum and ally steel?? cast iron?? and stainless steel.</br><br/>http://www.amazon.com/gp/product/B000AEULWI