Features:
1) The housing is made of plastic / aluminum / zinc / pressed steel material 
    according to customers' requirements
2) The rollers outer ring is produced of plastic materials (POM, PP, PA, nylon) 
    or metal material, with excellent surface for sliding windows and doors
3) The inner ring is produced of carbon steel with zinc plated, with excellent
    resistance to corrosion capacity
4) The roller set with long life performance