One hardened steel SwiftTool Carbon0.6 for use with all kinds of filaments including abrasive filaments like proCarbon™ and proGlass™. The Carbon0.6 is marked by a black cable, so you easily can separate them from the other sizes.
There is also an upgraded version that is moulded into silicone to lessen the material sticking to the hot end and also protect the cable. You find it here (ZX726S).
ZYYX Pro: all models
ZYYX/ZYYX Classic: NO