قطعة الغيار هنا.

Because Arabic usually does not use a present-tense verb meaning to be in simple sentences like this.

So:

• قطعة الغيار هنا = The spare part is here

There is no separate word for is in the present tense.

This kind of sentence is called a nominal sentence in Arabic.

Compare:

• قطعة الغيار هنا = The spare part is here
• كانت قطعة الغيار هنا = The spare part was here

So in the present, Arabic normally leaves is/am/are unspoken.

Yes. قطعة الغيار is a single noun phrase.

It is an iḍāfa (also called a construct phrase), which is a very common Arabic pattern:

• قطعة = piece / part
• الغيار = replacement / spare

Together, they mean the spare part.

A useful point for English speakers: Arabic often uses noun + noun where English uses adjective + noun.

So instead of something exactly like:

• spare part

Arabic uses something more like:

• part of replacement
• or more naturally: spare part

So الغيار here is not really an adjective like English spare. It is part of an iḍāfa phrase.

This is because of how iḍāfa works.

In an iḍāfa:

• the first noun does not take الـ
• the second noun can be definite or indefinite
• the definiteness of the whole phrase depends on the second noun

So:

• قطعة غيار = a spare part
• قطعة الغيار = the spare part

Even though قطعة has no الـ, the whole phrase is definite because الغيار is definite.

This is completely normal in Arabic.

Because قطعة ends in ة (tāʾ marbūṭa), and that ending is often pronounced as -t when the word is connected to what follows in an iḍāfa.

So:

• by itself: قطعة is usually pronounced roughly qiṭʿa
• in قطعة الغيار: it becomes qiṭʿat al-ghiyār or, with full case endings, qiṭʿatu l-ghiyāri

So the t sound appears because the word is not being said in isolation.

A common pronunciation is:

qiṭʿat al-ghiyār hunā

In more formal fully inflected MSA, it would be:

qiṭʿatu l-ghiyāri hunā

A few pronunciation notes:

• ق = a deep q sound, not exactly English k
• ط = an emphatic t
• غ = gh, a sound not native to English; it is similar to the French or Parisian r for many learners
• هنا = hunā = here

If you are reading ordinary unvowelled Arabic, qiṭʿat al-ghiyār hunā is a very practical pronunciation to know.

هنا means here, and it functions as the predicate of the sentence.

So the structure is:

• قطعة الغيار = the spare part
• هنا = here

Literally, the sentence is:

• The spare part — here

Which English expresses as:

• The spare part is here

So هنا is giving the location of the subject.

In fully inflected MSA, the sentence would be:

قِطْعَةُ الغِيَارِ هُنَا

or transliterated:

qiṭʿatu l-ghiyāri hunā

Why?

• قطعةُ is the subject of the sentence, so it is nominative
• الغيارِ is the second part of the iḍāfa, so it is genitive
• هنا is indeclinable, so it does not change

In everyday speech and in most non-vowelled writing, these case endings are usually not written or pronounced clearly.

Yes, Arabic word order is somewhat flexible.

The neutral order here is:

• قطعة الغيار هنا = The spare part is here

You may also see:

• هنا قطعة الغيار

This can sound more like:

• Here is the spare part
• or it can put more emphasis on here

So the original order is straightforward and neutral, but other orders are possible for style or emphasis.

Here are the basic forms:

• قطعة غيار = a spare part
• قطعة الغيار = the spare part
• قطع غيار = spare parts
• قطع الغيار = the spare parts

Notice something important:

• singular: قطعة
• plural: قطع

But غيار stays the same in this common expression.

So if you want to build similar sentences:

• قطعة غيار هنا = A spare part is here / There is a spare part here
• قطع الغيار هنا = The spare parts are here

It is a complete sentence.

Why?

Because Arabic can make a full sentence out of:

• a subject: قطعة الغيار
• plus a predicate: هنا

That is enough to form a complete present-tense statement.

So even though it may look short to an English speaker, it is not just a fragment. It is a normal Arabic sentence.