If your derailleur is unprotected, a rear derailleur protector is definitely worth purchasing.The Derailleur chain stay guard protects the rear derailleur from being hit or shifted while riding! The Rear derailleur protector is very easy to install and protects the derailleur in the event of a fall. It is perfect for children's bikes such as mountain bikes or MTBs! The Rear derailleur guard is 7mm thick and really protects the rear derailleur. The guard appears to be made of sturdy steel, which definitely minimizes any potential damage in the event of an accident! Rear derailleur guards fit directly onto the axle bolts and work so well that you can fit them to all bikes! UNIVERSAL SIZE: Derailleur chain stay guard shaped to fit most mountain bikes, road bikes, and folding bikes, effectively protects the rear derailleur from derailment