Our J Head compatible extruder is based on the original J Head extruder (http://reprap.org/wiki/J_Head_Nozzle).The set we sell is based on the version 4 nozzle and version 5 nozzle holder.
The max operational temperature is 247 degrees as the peek will start to become some at this point. However, approaching this point you should already be carefull not to use to much force or the nozzle may be pushed out of the holder.
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