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If NFDM is read as an initialism (pronouncing each letter: "en-eff-dee-em"), use : An NFDM-225 z R-- If NFDM is read as a single word or brand name (e.g., "Nifdim"), use "a" : A NFDM-225 z R-- However, since acronyms like NFDM are most often pronounced as separate letters, "an" is the safer and more standard choice.
The phrase appears to be a technical or model designation, likely from a Polish-language context (given the use of "z" meaning "from" or "with"). The proper article in English depends on how you read the acronym NFDM. NFDM-225 z R--