描述了使用圆形（圆形）和方形穿孔的三种图案。方孔的尺寸范围为2 mm，圆孔的尺寸范围为0.5 mm。规定了五个螺距与孔的比率，其导致标称开放面积在约60%到23%之间。

Describes three patterns using round (circular) and square perforations. The sizes of holes range down to 2 mm for square holes and to 0.5 mm for round holes. Five ratios of pitch to hole are specified which result in nominal open areas ranging from about 60 % to 23 %.