Old style bolts with a slight dome. Machined from 4142 steel that is heat treated equivalent to Grade 5. The correct style for many vintage vehicles. 

Black Oxide finish

size-1/4-28x3/4        A) 3/4"    B) 5/8"     C) .270"  D) 7/16" - NUT304

size- 1/4-28x1           A) 1"       B) 3/4"     C) .270"  D) 7/16" - NUT305

size - 1/4-28x1-1/4   A) 1-1/4" B) 1-1/4" C) .270    D) 7/16" - NUT762

size - 1/4-28x1-1/2   A) 1-1/2" B) 7/8"     C) .270"  D) 7/16"  -NUT306