Hitachi 728267 1-inch x 18-inch Auger Drill Bit (Discontinued by the Manufacturer) 1-inch by 18-inch auger drill bit with 3/8-inch shank diameter Precision design creates less wobble in the drill and bit Self-feeding tip and wide throat leave cleaner holes Ideal for wood, plastic and metal,Comes with a 30-day limited warranty 3/8 dimension for the shank measures from flat side to opposite flat side (not from the corners). 1" x 18" Auger Bit 3/8" shank Precision design High speed steel Wood or Plastic