A threaded fastener having a threaded portion with a ratio of pitch diameter to minor diameter less than 1.28, and the threaded portion with a major diameter portion, a leading flank having a normal angle between 10° and 60°, a trailing flank having a normal angle between 1° and 30°, and a shank portion extending between the trailing flank and the leading flank of adjacent threads of a arcuate surface having a radius greater than the thread height. The arcuate surface forming the shank portion may have a radius between 1.2 and 1.8 times the thread height.