Sayı kilidi ve harf kilidi aynı kutuda.

• sayı = number
• harf = letter
• kilit = lock
• ve = and
• aynı = same
• kutu = box

So:

• sayı kilidi = number lock / numeric lock
• harf kilidi = letter lock / alphabetic lock
• aynı kutuda = in the same box

Because Turkish often forms noun compounds by adding the third-person possessive suffix to the second noun.

So:

• kilit = lock
• sayı kilidi = number lock
• harf kilidi = letter lock

The suffix here is basically -i, but kilit changes to kilid- before that suffix, so:

• kilit + i → kilidi

This sound change is very common in Turkish and is called consonant softening:

• t → d before a vowel in many words

So kilidi is not a different dictionary word; it is kilit with a suffix.

It looks possessive at first, but it is better understood as a noun compound.

In English, we often use one noun to modify another:

• school bus
• coffee cup
• door handle

Turkish does something similar, but the second noun usually takes a suffix:

• okul otobüsü = school bus
• kahve fincanı = coffee cup
• kapı kolu = door handle
• sayı kilidi = number lock

So sayı kilidi does not mean that a number literally owns the lock. It just means a lock related to numbers.

Kutuda means in the box or inside the box.

It is made of:

• kutu = box
• -da = a location suffix meaning in / on / at

So:

• kutuda = in the box

This suffix is called the locative.

More examples:

• evde = at home / in the house
• masada = on the table
• arabada = in the car

The locative suffix changes form because of vowel harmony and consonant harmony.

The locative has four possible forms:

• -da
• -de
• -ta
• -te

In kutu, the last vowel is u, which is a back vowel, so the suffix uses a/e harmony and becomes -da rather than -de.

Also, kutu ends in a vowel, so there is no reason for the d to change to t.

So:

• kutu + da → kutuda

Compare:

• evde = in the house
• parkta = in the park
• okulda = at school

In Turkish, the verb to be is often left out in simple present-tense sentences, especially in the third person.

So Turkish can say something that is literally more like:

• Number lock and letter lock same box-in

but the natural English meaning is:

• The number lock and the letter lock are in the same box.

This is completely normal in Turkish.

Examples:

• Ali evde. = Ali is at home.
• Kitap masada. = The book is on the table.
• Onlar burada. = They are here.

Because aynı kutu only means the same box as a noun phrase.

But the sentence needs a location:

• in the same box

That is why Turkish adds the locative ending:

• aynı kutuda = in the same box

So:

• aynı kutu = the same box
• aynı kutuda = in the same box

Aynı means same and comes before the noun it modifies.

So:

• aynı kutu = the same box
• aynı ev = the same house
• aynı kişi = the same person

In this sentence, aynı describes kutu, not kilit.
So the meaning is that both locks are in one shared box.

Yes. That would also be grammatical.

• aynı kutuda = in the same box
• aynı kutunun içinde = inside the same box

The version with kutuda is shorter and very natural.
The version with kutunun içinde is a little more explicit.

So both can work, but aynı kutuda is the more compact everyday phrasing.

Because the sentence is talking about two separate things:

• sayı kilidi
• harf kilidi

If you remove the second kilidi, the meaning changes or becomes less clear.

For example:

• sayı ve harf kilidi could sound like a number-and-letter lock or one lock associated with both numbers and letters, rather than two separate locks.

Repeating kilidi makes it clear that there are two locks being mentioned.

This word order is the most neutral and natural:

• Sayı kilidi ve harf kilidi aynı kutuda.

Very roughly, it follows:

• subject + subject + location

Turkish word order is flexible, but different orders can sound more marked or give special emphasis.

For a learner, this sentence is a good standard pattern:

• X ve Y aynı yerde. = X and Y are in the same place.

Examples:

• Ali ve Ayşe bahçede. = Ali and Ayşe are in the garden.
• Anahtar ve telefon çantada. = The key and the phone are in the bag.

Turkish does not have articles like English a/an/the.

So Turkish often leaves that information to context.

That means:

• kutu can mean a box or the box, depending on context
• kilit can mean a lock or the lock

In this sentence, aynı already makes the box feel specific:

• aynı kutuda = in the same box

So English usually needs an article, but Turkish does not.

The Turkish ı is the dotless i, and it is different from English i.

It is pronounced far back in the mouth, somewhat like the vowel in the second syllable of roses for some English speakers, but that is only an approximation.

In this sentence:

• sayı sounds roughly like sa-yuh with a back vowel at the end
• aynı sounds roughly like eye-nuh with that same back vowel

A few important points:

• i and ı are different letters in Turkish
• i = a front vowel
• ı = a back, unrounded vowel

So learners should try to hear the difference between:

• dil
• dıl if it existed as a contrast

In your sentence, noticing ı correctly will help your pronunciation sound much more natural.