Standard Penetration Test. The number of blows required to drive a 2-inch O.D., 1-3/8 inch I.D., 24-inch long, split soil sampling "spoon" 1 foot with a 140 pound weight freely falling 30 inches. The count is recorded for each of three 6-inch increments. The sum of the second and third increments is taken as the N value in blows per foot. (This is ASTM Designation D 1586).