6 Busch Twist Drill Bits Great for Metalsmiths, Metal Working & Drilling. This is a new set of 6 twist drill bits. Long time jewelers favorite. Made in Germany with a reputation for quality. These have an ISO of 006. Each shank measures 3/32" (2.3 mm). Each bit is a size 4/0 and measures approximately 0.6 mm in diameter.