El eje está en la rueda.

Because estar is used for location.

In El eje está en la rueda, the sentence tells you where the axle/shaft is, so Spanish uses estar:

• está = is (located)
• es = is (identity, description, classification, etc.)

So:

• El eje está en la rueda = the axle is in the wheel
• not El eje es en la rueda

Eje can mean several related things in Spanish, depending on context:

• axle
• shaft
• axis

In a sentence with rueda (wheel), the most natural meaning is usually axle or shaft, because that fits the mechanical context.

So even though eje can also mean axis in other situations, here it is probably understood as a mechanical part.

Spanish uses articles much more often than English does.

So where English might say:

• Axle is in wheel (which sounds unnatural in English anyway)
• or The axle is in the wheel

Spanish normally says:

• El eje está en la rueda

The articles el and la are not optional here in normal Spanish. They help make the sentence sound complete and natural.

Because Spanish nouns have grammatical gender:

• eje is masculine → el eje
• rueda is feminine → la rueda

This does not mean the objects themselves are masculine or feminine in a real-world sense. It is just part of how Spanish grammar works.

You usually need to learn nouns together with their article:

• el eje
• la rueda

That makes it easier to remember the correct gender.

En is a very common preposition that can mean in, on, or sometimes at, depending on context.

Here, en la rueda most naturally means:

• in the wheel
• or possibly on the wheel, depending on the exact physical situation

Spanish often uses en where English has to choose more precisely between in and on.

So the best translation depends on the context, but the Spanish itself is completely normal.

Yes, you could, but it changes the feel slightly.

• en la rueda = in/on the wheel, more general
• dentro de la rueda = inside the wheel, more explicit

If you want to emphasize that the axle is physically inside the wheel, dentro de can work. But en is simpler and very natural.

In Spain, eje is pronounced approximately like:

• EH-kheh, with the j as a strong throaty sound

More technically, the j is like the Spanish sound in jamón or José.

A rough guide:

• e as in bed (but cleaner)
• j as a harsh h/ch sound from the back of the throat
• e again the same way

So eje is roughly EH-kheh.

The accent mark is part of the correct spelling of the verb form está.

It is the third-person singular of estar in the present tense:

• yo estoy
• tú estás
• él/ella/usted está

The accent is important because esta without an accent is a different word, for example:

• esta rueda = this wheel

So:

• está = is
• esta = this

Yes, but El eje está en la rueda is the most neutral and natural order.

This is the normal pattern:

• subject + verb + place

You may sometimes see other orders for emphasis, for example:

• Está en la rueda el eje

But that sounds more marked or literary. For a learner, the standard form is best:

• El eje está en la rueda

Normally, no.

You would not usually say:

• Eje está en rueda

That sounds incomplete and ungrammatical in standard Spanish.

Spanish generally needs the articles here:

• El eje está en la rueda

So when you learn nouns, it is a good habit to learn them with their article.

Usually rueda means wheel, especially in everyday and mechanical contexts.

It can also appear in other expressions or more figurative uses, but in this sentence the normal meaning is definitely wheel.

So for this sentence, you can safely understand:

• la rueda = the wheel

Yes, Spanish often omits subjects, because the verb form already gives information.

For example, if the context were clear, someone might say:

• Está en la rueda

That could mean It is in the wheel.

But in your sentence, the speaker includes the subject El eje to make it clear exactly what is being talked about:

• El eje está en la rueda

So the full sentence is clearer and more explicit.

Not especially. El eje está en la rueda is standard Spanish and would be understood across the Spanish-speaking world.

The main Spain-specific point here is pronunciation:

• in Spain, the j in eje is pronounced with the usual strong Spanish j sound

But grammatically and vocabulary-wise, the sentence is standard and widely used.