SODIAL(R) Mech Cycling Bike Iron Bicycle Rear Gear Derailleur Chain Stay Guard Protector-black The shape conforms to most of the mountain bike,to provide effective protection for rear derailleur prevent the derailleur was struck distortion or displacement in riding to ensure the safety of the riding. Can also be used protect rear derailleur when tripped,is very reliable. Left and right wings slot,can be more fastness install on the frame. Single fixed hole can be easily installed.