Please Note this is the 7.5FT model.【Notice】If you have enough ceiling space for 9'', we suggest you buy double track bypass, the 2 doors are independently slide on track of each other, search ASIN number B06XKLTPHK 【Notice】This is single track bypass, one track hang 2 doors, the roller diameter is 2-1/5'', so the door will be have 7''-8'' distance overlap, so please let your door bigger than your opening, the 2 rollers will be hit together when one door slide, maybe drive other door slide 【Main Material & Surface】Black frosted（Multiple electrostatic powder spraying process）, high quality carbon steel (High Standard Q235), corrosion protection, antirust，environmental protection, non-pollution. 【Design】Track's hole: standard 16 inches. Track and roller arm thickness: 1/4 inches, very sturdy. Track and door bolts is 8.8 grade high strengh bearing capacity. Stopper: rubber covered, good buffer effect, reduce the noise.The wheel surface is covered with nylon, slide very quietly. 【Core Parts】Roller Bearing is high purity bearing steel Gcr15, passed the test of opening - closing for 100000 times, wear-resisting, ensure the stability of the move and the wheel's fluency. Wheel shaft is made of reinforced steel and electrophoretic process, These are different from other products