The bontrager hollow 6mm bottle cage formed using 6mm hollow 6061 t6 aluminum tubing this lightweight and economical cage has a durable powder coat finish designed to keep it looking good bontrager hollow 6mm bottle cage features 6061 t6 aluminum rod with two piece bracket durable powder coat finish special design fits over front derailleur bands 30 second installation limited lifetime warranty hollow tubing eliminates 15 grams of weight without loss of strength