Most modern frames have an integrated gear hanger. This may be part of the actual frame, if the frame is made of steel. If the frame is made of aluminium it’s more likely to be bolted on so it can be replaced if it gets damaged. Some older – or low budget – frames have a hanger with a slot for the axle. This type clamps onto the slot where the back wheel fits, it has a small bolt and crescent-shaped nut that hold it in place when the wheel comes out and is held securely by the right side axle-nut of the rear wheel. In this case the hanger is either part of the rear derailer or a separate element.
Grease the threads in the hole in the gear hanger.
Screw On The Rear Derailleur
Introduce the fixing bolt of the rear derailleur into the hole in the hanger. The hanger has a tab on the back where the ‘C’ screw rests. Check the ‘C’ screw is in the right place to go past this tab without hitting it. Fully tighten the bolt to lock the derailleur to the bike.