Sprettekniven brukes under forandringssømmen i systuen.

Because it is the definite singular form of en sprettekniv.

In Norwegian, the definite article is usually attached to the end of the noun:

• en sprettekniv = a seam ripper
• sprettekniven = the seam ripper

This is very common in Norwegian and often feels unusual to English speakers at first, because English uses a separate word like the instead.

Yes. Sprettekniv is a compound noun:

• sprette = to unpick / rip open
• kniv = knife

So the word literally suggests a knife for unpicking stitches. Norwegian uses compound nouns very freely, much more than English does, and they are normally written as one word, not two.

Brukes is the present passive form of å bruke.

• å bruke = to use
• bruker = uses / is using
• brukes = is used / gets used

So Sprettekniven brukes ... means The seam ripper is used ...

Norwegian has a very common passive form made with -s. English usually needs extra words such as is used, but Norwegian can often do it in one word.

You could also make a passive with blir brukt, but brukes is very natural in general statements like this.

Yes. It is present tense passive.

That often translates naturally into English as something general or habitual:

• Den brukes ofte. = It is often used.
• Sprettekniven brukes ... = The seam ripper is used ...

So this sentence sounds like a general fact about how the tool is used.

Not necessarily. Under can mean underneath, but it can also mean during or in the course of.

In this sentence, the intended meaning is more like:

• during
• while doing
• in the course of

So under forandringssømmen is better understood as during the alteration work rather than physically underneath the alteration seam.

It is another compound noun. It is built from:

• forandring = change / alteration
• linking -s-
• sømmen = the sewing / the seam

So forandringssømmen is a specialized sewing-related compound. Norwegian often builds long nouns this way.

A native English speaker often expects spaces, but Norwegian usually joins these elements together into a single word.

That -s- is a linking element used in many Norwegian compounds.

So:

• forandring
• • s
• • søm

becomes forandringssøm

This -s- does not usually have a separate meaning by itself. It is just part of how compounds are formed. English learners often notice it because it can look like a plural or possessive marker, but here it is neither.

For the same reason as sprettekniven: it is in the definite singular form.

• en søm = a seam / a piece of sewing
• sømmen = the seam / the sewing

In the full compound:

• forandringssøm = alteration sewing / alteration seam
• forandringssømmen = the alteration sewing / the alteration seam

So both major nouns in the sentence are definite:

• sprettekniven
• forandringssømmen

The definite form suggests a specific, understood piece of work or process rather than alteration sewing in the abstract.

In context, it can mean something like:

• during the alteration work
• during that alteration sewing process

Norwegian often uses the definite form where English might sound more general or where English would rely more on context.

Systuen means the sewing room, the sewing workshop, or the tailoring room/shop, depending on context.

It comes from:

• sy = sew
• stue = room / parlor / workshop-like room in some compounds

So:

• en/ei systue = a sewing room / sewing workshop
• systuen = the sewing room / sewing workshop

The ending -en marks the definite form here.

Good question. In Bokmål, many feminine nouns can take either:

• -a
• or -en

So both of these may be possible depending on style:

• systua
• systuen

The version in your sentence uses systuen, which is perfectly normal Bokmål. English speakers often notice this because Norwegian has some flexibility here that English does not.

Yes, it is very normal.

The structure is:

• Sprettekniven = subject
• brukes = verb
• under forandringssømmen = prepositional phrase
• i systuen = prepositional phrase

So the sentence follows a straightforward pattern:

Subject + verb + extra information

Nothing unusual is happening with the word order here.

Yes. A common alternative would be a passive with bli:

• Sprettekniven blir brukt under forandringssømmen i systuen.

That also means The seam ripper is used during the alteration work in the sewing room/workshop.

Very roughly:

• brukes often sounds compact and matter-of-fact
• blir brukt can sound a little more explicit

Both are grammatical, but the -s passive is especially common in short factual statements like this one.

Absolutely. This sentence is a very good example of a major feature of Norwegian.

You have several compounds here:

• sprettekniv
• forandringssø m
• systue

Norwegian regularly combines smaller words into one larger noun. For English speakers, one of the most useful habits is to learn to break compounds apart and identify their pieces. That makes long words much less intimidating.