You recognise the 146 primarily by its size: closed about 14.5 cm long with a Meisterstück ring of about 1.5 cm diameter. The filling system is a permanently fitted piston filler, no converter and no cartridge system; it is operated by turning at the rear end. The term 'piston converter' is used by some for the permanently fitted mechanism; more correct is the designation piston pen, since converters must always be exchangeable. Cartridges are taken only by the 147 Traveller; the 145 Chopin uses an exchangeable converter. Classic piston pens have, by the state of the discussion, practically not been counterfeited.
Related pages on fountainpen.de:
• Montblanc Meisterstück 146 (Le Grand): https://www.fountainpen.de/c-montblanc-meisterstueck-146-en.htm