we stock 5mm derailer and brake housing for the most part. 4mm shimano housing is used occasionaly for the newer finicky shimano 10spd stuff. 5mm ferules come in two flavors, one for brake and one for index or derailer housing. brake ferules are low quality and should be avoided. i only use the derailer style ferules for the 5mm housing. give your ferules a quick squeeze between the thumb and index finger to check the quality. the brake ferules will just collapse. derailer ferules have thicker walls and bottoms.