Fabrička greška nije mehaničko oštećenje.

Because Serbian adjectives must agree with the nouns they describe in gender, number, and case.

• greška is feminine singular nominative, so the adjective is fabrička
• oštećenje is neuter singular nominative, so the adjective is mehaničko

So the different endings are not random—they show agreement with the noun.

Both are in the nominative singular.

• fabrička greška is the subject
• mehaničko oštećenje is the predicate noun phrase after nije

In Serbian, with sentences like X nije Y, the noun after biti is normally also in the nominative:

• Ovo je problem.
• Ovo nije problem.

So in this sentence, both noun phrases stay in the nominative.

Because nije is the standard negative form of je.

Compare:

• je = is
• nije = is not

Other negative forms are:

• nisam = I am not
• nisi = you are not
• nije = he/she/it is not
• nismo = we are not
• niste = you are not
• nisu = they are not

So nije should be learned as the normal form, not as two separate words.

Because Serbian has no articles.

English says:

• a factory defect
• the factory defect

Serbian simply says:

• fabrička greška

Whether it means a, the, or a general concept depends on the context. In this sentence, it sounds like a general statement or definition, not a reference to one specific defect.

Yes, it is a very common and natural expression. It is the standard way to talk about a manufacturing defect or factory defect.

So even though you can analyze it as:

• fabrička = factory / manufacturing-related
• greška = error / mistake / defect

together, fabrička greška functions as a familiar collocation.

Because oštećenje belongs to a very common Serbian neuter noun pattern. Nouns ending in -nje or -enje are often neuter.

Examples:

• pitanje = question
• rešenje = solution
• oštećenje = damage

This type of noun often names an action, result, or state. Here, oštećenje refers to the result/state of being damaged.

They are related, but not the same.

• greška is an error, fault, defect, or mistake
• oštećenje is damage, especially physical damage

So the sentence contrasts two ideas:

• a problem that comes from production/manufacture
• damage caused by mechanical force or impact

That distinction is exactly why the sentence is useful in product, warranty, or repair contexts.

Yes, Serbian word order is fairly flexible, although the given version is the most neutral.

Neutral order:

• Fabrička greška nije mehaničko oštećenje.

You could also say:

• Mehaničko oštećenje nije fabrička greška.

That keeps the same basic meaning, but shifts the focus a little. The first version starts from fabrička greška; the second starts from mehaničko oštećenje.

What usually stays together is the adjective + noun pair:

• fabrička greška
• mehaničko oštećenje

These are important Serbian sounds:

• č as in fabrička: a hard ch sound, similar to ch in chocolate
• ć as in oštećenje: a softer sound, somewhat like a very soft ty/ch sound; English does not have an exact equivalent
• š as in oštećenje: like sh in shoe

So:

• fabrička has the harder č
• oštećenje has both š and the softer ć

Because Serbian, like English, uses the present tense for general truths, definitions, and classifications.

So Fabrička greška nije mehaničko oštećenje means something like a general rule or category statement: X is not Y.

This is completely normal Serbian usage.

It would be:

Фабричка грешка није механичко оштећење.

Serbian commonly uses both scripts, so it is useful to recognize both the Latin and Cyrillic versions of the same sentence.