Jackknife of suitable bolster plate is used must not exceed two, total ply must not exceed 15 millimeter, the jackknife of horizontal bolster plate is used must not exceed 3, thicker bolster plate should be put in lower level.

• 顺垫板重叠使用不得超过两块，总厚度不得超过15毫米，横垫板的重叠使用不得超过三块，较厚垫板应放在下层。