US Patent 10150205 Fastening tools with floating magnet sleeves

A fastener driving tool includes a shaft with a working region disposed at a first end of the shaft and configured to drive a fastener, a shank portion disposed proximate a second end of the shaft and configured to couple the shaft to a power tool, and a reduced diameter torsion zone disposed between the shank portion and the working region, the torsion zone extending from a first shoulder closer to the working region to a second shoulder closer to the shank portion. A length (L) and a radius (c) of the torsion zone have been optimized so that approximately half of breakages occur in the working region and approximately half of breakages occur in the torsion zone.