Hope e4 complete caliper the one piece caliper is cnc machined from a solid billet of 2014 t6 aircraft spec aluminium alloy the e4 caliper uses four identical 16mm phenolic pistons which gives more usable power to the brake whilst keeping our ledgendary feel features four identical 16mm phenolic pistons cnc machined from a solid billet of 2014 t6 aircraft aluminium for durability and reduced weight weight from 400g buy hope e4 complete caliper from chain reaction cycles the worlds large