The bopworx bicycle protection rear derailleur guard is the best solution for protecting your rear derailleur and derailleur hanger during travel and storage covering your rear derailleur with a protective steel arm and semi soft rubberized paddingsimply loosen the quick release insert the guard and close the quick release to hold firmly in place made of steel and a very tough plastic it will protect your bike and rear derailleur from strong side impactsusing the rear derailleur guard in