Irwin Tools 3521111C 8-10Sl Power Bit, Fastener Drive, 1-15/16" Insert bits can be used for common round, oval and flat-head fasteners Insert bits are manufactured with industrial-grade S2 steel for maximum life and durability Each insert bit is designed for use in power drill chucks and chuck adapters Screwdriver bits feature a 8-10 point size 1/4" shank diameter