Also known as mini-grid porous grid, the use of staggered grid prevents small tools and other items through the hole fell into the ground, in line with the European 15mm ball test. The structure is equivalent to two different types of boxes stacked grille. We currently have two design imperial and metric. 
 Such a grid, although the design of horizontal and vertical Vitex is exactly the same, use the trapezoidal cross-section and the standard separation; However, each of its two adjacent ribs, only one is the same height and the grid, really bear load. We only carry these ribs called ribs.