Stihl 4313-680-3002 3.5 inch 90mm Auger Bit Replacement Head. STIHL Auger Bits are built and designed with durability in mind. Every bit design is tested, by STIHL, in a variety of soils across the country. Bit heads are cast from a single piece of heat-treated alloy for outstanding durability and drilling performance. The cutter heads are easy to remove and feature an offset tooth, instead of an installed plate, to improve drilling performance and avoid lockups. It all adds up to quality that doesn’t compromise – not one bit.