Innfatningen må passe til brilleglasset.

Because -en is the definite singular ending for many masculine nouns in Bokmål.

• innfatning = frame / setting / mounting
• innfatningen = the frame

So innfatningen means the frame.

A small extra point: although innfatning ends in -ing, which is often feminine, many such nouns can also be used as masculine in Bokmål. That is why you may see innfatningen. In some contexts, some speakers might also use a feminine form, but innfatningen is completely normal.

Here innfatning means the frame or mounting that holds the lens.

In ordinary glasses vocabulary, it refers to the part of the glasses that the lens goes into. Depending on context, English might translate it as:

• frame
• rim
• mounting

So in this sentence it is not a general decorative frame, but specifically the eyeglass frame part that has to fit the lens.

Because brilleglass is a compound noun meaning eyeglass lens.

It is made from:

• brille = glasses
• glass = glass / lens

Together, brilleglass means the lens used in glasses.

Then the definite singular form is:

• brilleglass = a lens
• brilleglasset = the lens

So brilleglasset does not mean the whole pair of glasses. It means the lens.

Because brilleglass is a neuter noun, and many neuter nouns take -et in the definite singular.

• et brilleglass = a lens
• brilleglasset = the lens

Compare:

• et hus → huset
• et glass → glasset
• et brilleglass → brilleglasset

So the ending -et tells you it is definite singular.

Here må means must or has to.

So:

• må passe = must fit / has to fit

It expresses necessity. The idea is that the frame cannot be used unless it fits the lens.

A useful comparison:

• må = must / have to
• kan = can
• skal = will / shall / is going to (depending on context)

In this sentence, må is the natural choice because the sentence is about a requirement.

Because passe til often means fit, match, or go with something.

In this sentence:

• passe til brilleglasset = fit the lens / be suitable for the lens

The preposition til is important here because it shows what the frame has to fit or match.

Useful comparisons:

• Det passer. = That works / That fits.
• Skoene passer. = The shoes fit.
• Skoene passer til kjolen. = The shoes go with the dress.
• Innfatningen passer til brilleglasset. = The frame fits the lens.

So passe alone can sometimes mean fit, but passe til is very common when you specify what something matches or is suitable for.

No. Passe til can be used in several related ways:

1. Physical fit

   • Innfatningen passer til brilleglasset.
   • The frame fits the lens.

2. Match in style or appearance

   • Den røde jakken passer til skoene.
   • The red jacket goes with the shoes.

3. Be suitable for

   • Denne boka passer til nybegynnere.
   • This book is suitable for beginners.

So in your sentence, the meaning is probably a physical/technical fit, but the same expression is used more widely.

Because this is a normal main clause in Norwegian, and the usual pattern is:

subject + finite verb + infinitive/main verb + rest

Here:

• Innfatningen = subject
• må = finite verb
• passe = infinitive/main verb
• til brilleglasset = prepositional phrase

So the structure is:

Innfatningen + må + passe + til brilleglasset

This is very similar to English:

The frame + must + fit + the lens

Usually, no—not in standard usage for this meaning.

Passe til is the normal expression when you mean:

• fit
• match
• be suitable for

So Innfatningen må passe til brilleglasset is the natural phrasing.

If you remove til, it sounds wrong or at least unnatural in this context.

Yes, both are singular:

• innfatningen = the frame
• brilleglasset = the lens

This sentence is talking about one frame and one lens.

If you wanted plurals, you could say:

• innfatningene = the frames
• brilleglassene = the lenses

For example:

• Innfatningene må passe til brilleglassene.
• The frames must fit the lenses.

Because the sentence is likely referring to specific items already known in the situation: the frame and the lens.

That is very normal in Norwegian, just as in English:

• the frame
• the lens

If you wanted a more general statement, you might use indefinite forms, for example:

• En innfatning må passe til et brilleglass.

But that sounds more like a general rule stated in isolation. The original sentence sounds like it is about a particular frame and a particular lens.

Yes, this is standard Bokmål, and it would be understood without any problem.

The vocabulary is normal and clear. Some speakers might choose slightly different everyday words depending on region or situation, especially for glasses-related terms, but this sentence is perfectly standard.

A careful pronunciation would be roughly:

Innfatningen må passe til brilleglasset.

A learner-friendly approximation might be:

INN-fat-ning-en moh PASS-uh til BRILL-uh-glahs-set

A few helpful notes:

• å in må is like the vowel in British law or more, but shorter depending on speech.
• passe has two syllables: PAS-se
• brille has a clear brill- sound
• glasset has a short vowel and double consonant feeling: glas-set

The exact pronunciation varies by dialect, but this approximation will help you recognize and say it.

Not always.

Innfatning often means some kind of mounting, setting, or frame-like holder. The exact English word depends on context.

For example:

• with glasses: frame
• with jewelry or stones: setting
• with lenses or technical parts: mounting or frame

So in your sentence, frame is the best natural English choice, but the Norwegian word itself is a little broader than that.