The Wallace has an X-Carriage that is very low... If you're using a J-Head with a slot-mount, the nozzle might not reach the bed before the carriage touches it... unless you mount the slot-mount plate UNDER the carriage. This adapter fills the gap between the extruder and the J-Head Nozzle Holder if you decide to mount the slot-mount plate under the carriage. These instructions are for: 1: Print and finish. Remove any support and use a dremel grinding stone cylinder (like the Dremel #932) to clean up the hole where the nozzle holder is going to be inserted. Use a drill bit or a tap (M4) to clean up the filament path. 2: Insert the J-Head nozzle holder into the large hole. 3: Mount the J-Head & Gap Adapter to the Slot-Mount plate. 4: Bolt the plate to the BOTTOM of the Wallace X-carriage. Use M4x25mm screws. 5: Place M4 nuts into the base of the extruder, and mount the extruder on TOP of the X-carriage and Gap Adapter. Tighten the M4 screws into the M4 nuts.