The water washing screening range is 37.5 to 19mm, 19 to 9.5mm, 9.5 to 4.75mm and below 4.75mm. According to the query of relevant public information, different uses have different requirements for the particle size gradation of gravel. Infrastructure screening must be carried out in strict accordance with the standards into several groups of gravel with different particle sizes: 37.5 to 19mm, 19 to 9.5mm, 9.5 to 9.5mm. There are four groups for gravel of 4.75mm and below 4.75mm.