These CRL Electro-Formed Diamond Drills are thin-walled, with a 1/2" (12.7 mm) deep multi-layer of diamonds and bonding matrix designed for high speed, high production drilling. These drills give outstanding results when exacting conditions are met. The CRL DCD Series features an extra long 1-3/8" by 3/8" (35 by 10 mm) diameter shank for a positive grip on the drill. The CRL HBT Series features Belgian style mounting threads, also known as 1/2" (12.7 mm, gas thread), which are popular choices for U.S. and European glass drilling machines.