Die Türklinke und der Reißverschluss sind beide alt, aber nur der Reißverschluss stört mich wirklich.

Because in German, all nouns are capitalized. That includes common nouns like Türklinke, Reißverschluss, and even abstract nouns.

So in this sentence:

• Türklinke and Reißverschluss are capitalized because they are nouns
• alt, beide, nur, and wirklich are not capitalized because they are not nouns

This is a basic but very important German spelling rule.

German nouns have grammatical gender, so each noun uses a specific article:

• die Türklinke = feminine
• der Reißverschluss = masculine

This is something you usually need to learn together with the noun.

A helpful pattern here is that compound nouns usually take the gender of the last part:

• die Klinke is feminine, so die Türklinke is feminine
• der Verschluss is masculine, so der Reißverschluss is masculine

So the final part of the compound often tells you the gender.

German uses compound nouns very often.

• Türklinke = Tür
  • Klinke
    Literally, door handle
• Reißverschluss = Reiß
  • Verschluss
    Literally something like zip fastener or pull-fastener, though in normal English we just say zipper

In German, the last part of a compound usually gives the basic category of the word:

• A Türklinke is a kind of Klinke
• A Reißverschluss is a kind of Verschluss

Because the subject is plural.

The subject is:

Die Türklinke und der Reißverschluss

That means the door handle and the zipper — two things. Since there are two items joined by und, German uses the plural verb:

• singular: Die Türklinke ist alt
• plural: Die Türklinke und der Reißverschluss sind alt

So sind is correct because the subject is plural.

Because alt is being used as a predicate adjective, after the verb sein.

In German, adjectives after sein, werden, and bleiben usually do not take endings:

• Die Türklinke ist alt
• Der Reißverschluss ist alt
• Die Türklinke und der Reißverschluss sind alt

But if the adjective comes before a noun, it does take an ending:

• die alte Türklinke
• der alte Reißverschluss

So:

• alt after sind → no ending
• alte / alter before a noun → adjective ending required

Beide means both.

So:

sind beide alt = are both old

It tells you that the statement applies to both nouns, not just one.

The position is natural, but not the only possible one. You could also say:

• Die Türklinke und der Reißverschluss sind beide alt
• Die Türklinke und der Reißverschluss beide sind alt — not natural
• Beide sind alt — possible if the two things are already clear from context

In this sentence, sind beide alt sounds very normal and idiomatic.

Because after aber, you get a new main clause, and German main clauses follow the verb-second rule.

The clause is:

nur der Reißverschluss | stört | mich wirklich

So:

1. first position: nur der Reißverschluss
2. second position: stört
3. then the rest: mich wirklich

A key point: aber does not count as the first position inside the clause. It just connects two main clauses.

That is why German says:

• ..., aber nur der Reißverschluss stört mich wirklich

and not something like:

• ..., aber nur der Reißverschluss mich wirklich stört in a normal main clause

Here nur modifies der Reißverschluss.

So the meaning is:

• only the zipper really bothers me

In other words:

• the door handle is also old
• the zipper is also old
• but only the zipper is actually a problem for me

Because nur comes directly before der Reißverschluss, it strongly attaches to that noun phrase.

Because the verb stören takes an accusative object.

So:

• Der Reißverschluss stört mich = The zipper bothers me

Here:

• der Reißverschluss is the subject
• mich is the accusative object

This is different from some other German verbs that use the dative. For example:

• Das gefällt mir = I like that

But with stören, you use accusative:

• Das stört mich
• Der Lärm stört mich
• Nur der Reißverschluss stört mich wirklich

Stören means to bother, to disturb, or to annoy depending on context.

In this sentence, it means something like:

• to bother me
• to be a real problem for me

So nur der Reißverschluss stört mich wirklich means that the zipper is the thing that genuinely bothers the speaker.

It is a very common verb in German:

• Entschuldigung, störe ich? = Sorry, am I disturbing you?
• Der Lärm stört mich = The noise bothers me

Because repeating the noun makes the contrast clearer and stronger.

The sentence first mentions two things:

• die Türklinke
• der Reißverschluss

Then it says that only one of them is a real problem. Repeating der Reißverschluss makes that contrast very explicit.

You could say:

• ..., aber nur er stört mich wirklich

But that is less clear and slightly less emphatic, especially for learners or in a context where two masculine nouns might be possible. Repeating the noun is often the safest and most natural choice when making a contrast.

Wirklich means really.

It adds emphasis:

• stört mich = bothers me
• stört mich wirklich = really bothers me

So the speaker is saying that the zipper is not just theoretically old, but is the one thing that actually matters to them.

The placement is natural at the end of the clause. German adverbs like wirklich are somewhat flexible, but this position sounds very normal here.

Yes, absolutely.

That version is grammatically correct:

• Die Türklinke und der Reißverschluss sind alt, aber nur der Reißverschluss stört mich wirklich.

Adding beide just makes the meaning a little more explicit:

• sind alt = are old
• sind beide alt = are both old

So beide is not required, but it helps stress that the adjective applies equally to both items.