Sein Gürtel ist zu locker, deshalb zieht er ihn enger.

Because Gürtel is masculine singular: der Gürtel.

So in the nominative singular masculine, the possessive determiner is sein:

• sein Gürtel = his belt

This works like ein-words in German:

• ein Gürtel
• mein Gürtel
• sein Gürtel

If the noun were plural, you would get seine:

• seine Gürtel = his belts

Zu locker means too loose.

A useful distinction:

• locker = loose
• zu locker = too loose

So the sentence is not just saying the belt is loose; it says it is more loose than is acceptable or useful.

Examples:

• Das Hemd ist locker. = The shirt is loose.
• Das Hemd ist zu locker. = The shirt is too loose.

Because the sentence contains two main clauses:

1. Sein Gürtel ist zu locker
2. deshalb zieht er ihn enger

The comma separates those two clauses.

Also, deshalb is not a subordinating conjunction like weil. It introduces a new main clause, not a subordinate clause.

So the structure is:

• [main clause], deshalb [main clause]

Because German main clauses follow the verb-second rule.

In a main clause, the finite verb must be in the second position. If deshalb comes first, then the verb must come immediately after it:

• Deshalb zieht er ihn enger.

Not:

• Deshalb er zieht ihn enger. ❌

You can think of it like this:

• Position 1: deshalb
• Position 2: zieht
• then the subject: er

This is a very common German pattern:

• Heute gehe ich nach Hause.
• Dann rufe ich dich an.
• Deshalb zieht er ihn enger.

Deshalb means therefore, that’s why, or for that reason.

It gives a result/consequence:

• Sein Gürtel ist zu locker, deshalb zieht er ihn enger. = His belt is too loose, therefore he tightens it.

Weil means because and gives a reason/cause:

• Er zieht seinen Gürtel enger, weil er zu locker ist. = He tightens his belt because it is too loose.

Important grammar difference:

• deshalb starts a main clause → verb stays in second position
• weil starts a subordinate clause → verb goes to the end

Compare:

• ..., deshalb zieht er ihn enger.
• ..., weil sein Gürtel zu locker ist.

Zieht is the 3rd person singular form of ziehen.

Basic meaning of ziehen:

• to pull
• to draw

But with a belt, einen Gürtel enger ziehen means:

• to tighten a belt
• literally: to pull a belt tighter

So here zieht is best understood as pulls/tightens.

Related forms:

• ich ziehe
• du ziehst
• er/sie/es zieht
• wir ziehen

Ihn refers to den Gürtel.

Since Gürtel is masculine and it is the direct object of zieht, German uses the accusative masculine pronoun:

• der Gürtel → nominative
• den Gürtel → accusative
• pronoun: ihn

So:

• er = he
• ihn = him / it (for a masculine noun in the accusative)

In this sentence:

• er = the man wearing the belt
• ihn = the belt

English uses it, but German uses grammatical gender, so a masculine noun becomes ihn here.

Because German pronouns follow the grammatical gender of the noun, not the natural English idea of it.

• der Gürtel is masculine
• so in the accusative it becomes ihn

If the noun were neuter, then you would use es:

• das Buch → Er liest es.

But here:

• der Gürtel → Er zieht ihn enger.

So even though English says it, German says ihn because Gürtel is masculine.

Because enger is the comparative form of eng:

• eng = tight / narrow
• enger = tighter / narrower

Here it is being used predicatively/adverbially, not directly before a noun. That means it does not take adjective endings.

Compare:

• ein enger Gürtel = a tight belt
  → adjective before a noun, so it gets an ending
• Er zieht den Gürtel enger. = He pulls the belt tighter
  → no ending, because enger is describing the result of the action

So in this sentence, enger means tighter.

Yes, very much so.

Einen Gürtel enger ziehen is a normal German expression for tightening a belt.

There is also a broader idiomatic meaning:

• den Gürtel enger schnallen / enger ziehen

This can mean to cut spending or to live more frugally, similar to English to tighten one’s belt.

In your sentence, though, it is probably meant literally: the belt is too loose, so he tightens it.

Yes, in many situations you may hear:

• Er zieht den Gürtel fester.

That also means He tightens the belt.

Nuance:

• enger focuses more on making it tighter/narrower around the waist
• fester focuses more on making it firmer/tighter in hold

With a belt, both are natural, though enger ziehen is especially common.

In normal context, yes.

The most natural reading is:

• Sein Gürtel = his belt
• er = the same male person
• ihn = the belt

So the sentence means that his own belt is too loose, so he tightens it.

Technically, in a larger context, sein could refer to another male person, but without extra context, learners should understand it as the same person.

Not in standard German here.

German normally requires the subject pronoun er, and the object pronoun ihn is also needed because it tells you what he is tightening.

So:

• deshalb zieht er ihn enger = complete and normal

If you removed ihn, the sentence would sound incomplete or would need a different structure.

German usually keeps these pronouns where English might also keep them:

• He tightens it.
• Er zieht ihn enger.