هذا رقم الهيكل.

In Arabic, present-tense sentences like X is Y usually do not use a separate verb for to be.

So هذا رقم الهيكل literally looks like this chassis number, but in normal English it means This is the chassis number.

If you wanted a past-tense version, Arabic would use a verb, for example:

• كان هذا رقم الهيكل = This was the chassis number

Here, هذا stands by itself and means this.

So the sentence is structured like:

• هذا = this
• رقم الهيكل = the chassis number

Together: This is the chassis number.

If هذا were directly attached to a noun, it would mean this + noun, for example:

• هذا الرقم = this number

But in هذا رقم الهيكل, هذا is not directly modifying رقم. It is the subject of the sentence.

Because هذا is the masculine singular form of this, and it matches رقم, which is a masculine noun.

• هذا = masculine singular this
• هذه = feminine singular this

The important noun here is رقم meaning number, and رقم is masculine, so هذا is correct.

Because رقم الهيكل is an iḍāfa construction, often called a construct phrase.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun shows whether the whole phrase is definite

So:

• رقم هيكل = a chassis number or number of a chassis
• رقم الهيكل = the chassis number or number of the chassis

Since الهيكل is definite because of الـ, the whole phrase رقم الهيكل is also definite.

No. الهيكل is not an adjective here. It is a noun attached to رقم in an iḍāfa construction.

So رقم الهيكل literally means:

• number of the chassis

This is a very common Arabic pattern. English often uses noun + noun combinations, while Arabic often uses iḍāfa instead.

For example:

• باب البيت = the door of the house
• اسم الطالب = the student’s name
• رقم الهيكل = the chassis number

هيكل can mean things like structure, framework, skeleton, or chassis, depending on context.

In this sentence, the natural meaning is usually chassis, especially in car-related or official-document contexts. That is why رقم الهيكل is often translated as chassis number or sometimes VIN, depending on the exact situation.

A simple learner-friendly pronunciation is:

hādhā raqam al-haykal

A few useful sound notes:

• ذ in هذا sounds like th in this
• ر is a tapped or lightly rolled r
• خ is a throaty sound, like ch in Scottish loch or German Bach
• ال in الهيكل is pronounced al-, because ه is not a sun letter

In very formal MSA with full case endings, you may hear:

hādhā raqmu l-haykali

In fully vocalized MSA, it would be:

هذا رَقْمُ الهَيْكَلِ

Why?

• رقمُ is nominative, because it is the predicate of the sentence
• الهيكلِ is genitive, because it is the second noun in the iḍāfa

Many learners first meet the sentence without writing or pronouncing these endings, especially in everyday spoken MSA or less formal contexts.

Yes. هذا رقم الهيكل and هذا هو رقم الهيكل are both correct.

The version with هو is a little more explicit or emphatic, something like:

• This is the chassis number

The shorter version هذا رقم الهيكل is also completely normal and very common.