32 kinds of square nail, their breadth and thickness of cross section are 6-20mm, were tested. The relative difficulty of driving-the depth of the first driving, mean depth after second driving, number of driving up to the head-pulling power and lateral resistance are proportioned (the depth is inverse) to cross sectional area of nails. The mean unit pressure perpendicular to nail breadth is larger than pressure perpendicular to nail thickness and the former pressure is about 2/3 of mean unit holding power.