A must for the ends of brake and gear housing. Remember 5mm brake and gear housing ferrules are different. The gear ferrule has a smaller much finer hole. The brake ferrule cable hole is slightly bigger and not drilled with as much precision. Why you ask? Gear cable has many fine wires running the length of the housing. If a brake ferrule is installed on gear housing, the wires will eventually snake through the ferrule hole and either slow down or trap the cable. The 4mm gear ferrules we sell are black plastic press on's. Please choose wisely when ordering.