The models 144 and 145 are exclusively cartridge fillers; a piston filler is therefore either a 146 or a 149. The model number is not necessarily engraved on the middle ring, so the absence of such an inscription is no authenticity criterion. Piston fillers like 146 or 149 are because of the elaborate mechanism usually not counterfeited, unlike the 145, of which there are by now very good copies. With suspicion of a counterfeit, a detail photo of the nib is worthwhile, paying attention to flat-engraved script and correctly seated rings. In case of doubt one should refrain from the bid and request pictures from the seller.