... collapse during the return trip. 2,Base Belt Structure: Four Parts: Top cover rubber,bottom cover rubber, Reinforced core,Cross rigid.Thickness of ... top cover rubber:3-6 (mm)Thickness of bottom cover rubber: 1.5-4.5 (mm).Belt core: Nylon,EP, ... of collapse during the return trip. Base Belt Structure: Four Parts: Top cover rubber,bottom cover rubber, Reinforced core,Cross rigid.Thickness of ...