Trend CB38-316TC 3/16 drill diameter x 3/8 counterbore The CB counterbores are extensively used for recessing bolt and screw heads. Supplied with a HSS slow spiral drill bit. Fully adjustable, a hex key is supplied. TCT version is used for plywood, particle boards and plastics (abrasive). Use a drilling speeds only. Not suitable for ferrous and non-ferrous metals. When setting-up, ensure flutes of drill are aligned with flute of counterbore. For replacement Twist Drills, use slow spiral type e.g 501/532 to 501/012.