... , platforms grating , plain flooring grating , walkways grating , drain covers , and trench covers and filter grates , stair treads etc .grating dimension as follows : Bearing ... , 22mm ,34mm ,60mm, 80 mm , 90 mm of which 30mm and 40mm are recomended .2.crossing bar pitch from 38 mm ... mm , 76 mm, 100mm to 101.6mm of which 50mm and 100mm are recomended . trench cover