1)This product is extendable, mainly to solve the problem of measurement
2) 3 specifications to meet the requirements of different lengths, needn't precise sizes
3) Lao Zhu's is nano-silen, it is very smooth when sliding
4) The material is aluminium
5) The packing is 40SETS/Carton for single track, 20SETS/Carton for double track
6) It can be mounted either ceiling or wall
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