To build the Itty Bitty Double FLEX extruder, you will need: -Hardware kit (http://clough42.com/go/itty-bitty-double-extruder-hardware-kit) -Light extruder springs (optional for flexible filaments) (http://clough42.com/product/light-double-extruder-springs/) -Hobbed bolts (2) -Hot ends (2) -NEMA14 stepper motors (2) (http://www.pololu.com/product/1209) -HXT900 Servo (http://clough42.com/product/hxt900-servo/) -Z probe switch (recommended: http://www.digikey.com/product-search/en?KeyWords=SW1005-ND) -25x25x10 fan (for Hexagon hot ends) (recommended: http://www.digikey.com/product-search/en?KeyWords=259-1570-ND) -40x40x10 fan (for print cooling)