Dikiş yerinde bir fermuar dişi eksikti.

A natural breakdown is:

• dikiş = stitching, sewing, seam
• yeri = its place / place of
• dikiş yeri = seam area, seam line, the place where something is sewn
• dikiş yerinde = at the seam / in the seam area
• bir = a / one
• fermuar = zipper
• dişi = tooth
• fermuar dişi = zipper tooth
• eksikti = was missing / was absent / was lacking

So the whole sentence means something like:

A zipper tooth was missing at the seam.

Literally, it is closer to:

At the seam, a zipper tooth was missing.

Because yeri is not just yer.

Here, dikiş yeri is a noun phrase meaning the seam area or the place of the stitching. The word yeri contains the 3rd person possessive ending:

• yer = place
• yeri = its place / the place of it

Then the locative ending -de / -da is added:

• yeri + nde → yerinde

That n appears because Turkish often inserts a buffer n after a possessed noun before a case ending.

So:

• yerde = in/on the place
• yerinde = in/on its place, or in the place of something

In this sentence, dikiş yerinde means at the seam.

Literally, it means the place of stitching.

In actual usage, it refers to the part where something is sewn together, so depending on context it can mean:

• seam
• stitched area
• seam line
• place where the stitching is

So Dikiş yerinde is a very natural way to say at the seam or in the stitched area.

Because this is an indefinite noun compound, which is very common in Turkish.

Pattern:

• X Y-si = Y of X / X Y

So:

• fermuar dişi = zipper tooth
• literally: zipper tooth

In Turkish, this structure usually does not need the first noun to take the genitive ending.

Compare:

• kapı kolu = door handle
• araba kapısı = car door
• fermuar dişi = zipper tooth

If you say fermuarın dişi, that sounds more like the tooth of the zipper, which is grammatically possible in some contexts, but less neutral here. For naming the object type, fermuar dişi is the normal choice.

That -i is part of the indefinite noun compound structure.

In fermuar dişi:

• fermuar = zipper
• diş = tooth
• dişi = tooth + compound marker / 3rd person possessive-looking ending

This is the normal pattern for many Turkish compound nouns:

• kahve fincanı = coffee cup
• otobüs durağı = bus stop
• fermuar dişi = zipper tooth

So dişi here does not mean his/her tooth. It is just the standard form used in this compound.

Here it most naturally means a.

So:

• bir fermuar dişi = a zipper tooth

But Turkish bir can also mean one, depending on stress and context.

In this sentence, it is introducing an indefinite singular noun, so the English translation is usually a zipper tooth rather than one zipper tooth.

Because eksik means missing, lacking, or incomplete, while eksikti means was missing.

This is eksik + idi:

• eksik = missing / absent
• idi = was
• eksikti = was missing

In Turkish, idi often attaches directly to the word before it:

• hasta idi → hastaydı = was sick
• güzel idi → güzeldi = was beautiful
• eksik idi → eksikti = was missing

So the sentence is in the past because of -ti.

It starts as an adjective, but here it functions as the predicate of the sentence.

So in:

• bir fermuar dişi eksikti

eksikti means was missing.

Turkish often uses adjectives directly as predicates without needing a separate verb like to be in the present tense:

• Kapı açık. = The door is open.
• Parça eksik. = The part is missing.

In the past tense, Turkish adds the past form of to be:

• Kapı açıktı. = The door was open.
• Parça eksikti. = The part was missing.

This is a very typical Turkish sentence with the predicate at the end:

• Dikiş yerinde = at the seam
• bir fermuar dişi = a zipper tooth
• eksikti = was missing

So the structure is roughly:

location + subject + predicate

Turkish word order is flexible, but the neutral order usually puts the main predicate last.

Yes. Turkish allows some flexibility for emphasis.

For example:

• Dikiş yerinde bir fermuar dişi eksikti.
  Neutral and natural.

• Bir fermuar dişi dikiş yerinde eksikti.
  Also possible, with slightly different focus.

• Eksik olan, dikiş yerindeki bir fermuar dişiydi.
  More emphatic or stylistically different.

The original sentence is a normal, natural way to say it.

Yes. Diş literally means tooth, and Turkish uses it for many tooth-like parts, including the teeth of a zipper.

So:

• diş = tooth
• fermuar dişi = zipper tooth

This is similar to English, where tooth can also be used for gear teeth, comb teeth, zipper teeth, and so on.

The sentence is talking about one missing tooth, so singular is correct:

• bir fermuar dişi = a zipper tooth

If more than one tooth were missing, you might say:

• Birkaç fermuar dişi eksikti. = A few zipper teeth were missing.
• Fermuarın bazı dişleri eksikti. = Some of the zipper’s teeth were missing.

So the singular here is meaningful: it points to one missing tooth.

Yes. Eksik has a broad meaning that includes:

• missing
• lacking
• absent
• incomplete

Which English word fits best depends on context.

In this sentence, because it refers to a zipper tooth, missing is the best translation:

• bir fermuar dişi eksikti = a zipper tooth was missing

The noun phrase bir fermuar dişi is indefinite:

• bir = a
• fermuar dişi = zipper tooth

So it means a zipper tooth, not the zipper tooth.

If Turkish wanted to make it more definite, it would usually mark that differently, depending on context. But as written, the sentence introduces it as an indefinite item.

It is a locative phrase, showing location.

The core sentence is:

• bir fermuar dişi eksikti = a zipper tooth was missing

Then dikiş yerinde adds where this was the case:

• at the seam
• in the seam area

So it functions like an adverbial expression of place.