Al final saco el destornillador del cajón y cambio los tornillos por otros más largos.

Al final usually means in the end, eventually, or finally, depending on context.

In this sentence, it means something like in the end / finally: after other steps, this is what happens.

A useful distinction:

• al final = in the end / eventually
• al final de
  • noun = at the end of something
    
    • al final de la película = at the end of the film

So here, Al final saco... is not literally about the physical end of something like a book or film. It means this is the final action in the sequence.

Spanish often leaves out subject pronouns when they are clear from the verb ending.

• saco = I take out
• yo saco = I take out

The -o ending already tells you the subject is I (yo), so yo is usually unnecessary unless you want emphasis or contrast.

For example:

• Saco el destornillador... = neutral, normal
• Yo saco el destornillador... = I take out the screwdriver (maybe contrasting with someone else)

Spanish often uses the present tense to describe:

• a sequence of actions in a narrative
• instructions
• habitual actions
• a vivid, step-by-step description

So saco and cambio can sound like:

• I take out... and change... or, in natural English,
• I take out... and then replace...

This kind of present can make the action feel immediate, like the speaker is walking you through the process.

If you wanted a clearly past version, you could say:

• Al final saqué el destornillador del cajón y cambié los tornillos por otros más largos.

Here sacar means to take out or to get out.

So:

• saco el destornillador del cajón = I take the screwdriver out of the drawer

This is a very common verb when something is removed from a place.

Compare:

• sacar = take out, remove
• poner = put
• meter = put in, insert

In Spain, you may also hear coger for take, but sacar is more precise here because the screwdriver is being taken out of the drawer.

Because de + el contracts to del.

So:

• de + el = del
• a + el = al

That is why you get:

• del cajón = from the drawer
• al final = in the end / at the end

This contraction is required in normal Spanish, except when el is part of a proper name:

• de El Escorial stays de El Escorial

Spanish uses definite articles much more often than English.

So Spanish naturally says:

• el destornillador = the screwdriver
• los tornillos = the screws
• del cajón = from the drawer

Even when English might say I take out a screwdriver or simply I change screws, Spanish often prefers the article if the object is identifiable from context.

Here, the sentence sounds like the speaker has a particular screwdriver and particular screws in mind.

It means I replace the screws with longer ones.

Literally:

• cambio X por Y = I change X for Y / I swap X for Y

So:

• los tornillos = the original screws
• por otros más largos = for others that are longer

This is a very common pattern:

• cambiar una cosa por otra = to swap one thing for another
• cambiar los viejos por nuevos = replace the old ones with new ones

Because one common Spanish pattern is:

• cambiar algo por otra cosa = to exchange/replace something for/with something else

Examples:

• Cambio la camisa por otra. = I exchange the shirt for another one.
• Cambié las pilas por unas nuevas. = I replaced the batteries with new ones.

So in your sentence:

• cambio los tornillos por otros más largos

This does not mean because of here. The preposition por is part of the exchange/replacement structure.

Otros here means other ones.

It stands in for the noun tornillos, so Spanish does not need to repeat the noun:

• cambio los tornillos por otros = I replace the screws with others / with different ones

This is very common in Spanish.

Compare:

• Quiero otro. = I want another one.
• Necesito unas nuevas. = I need some new ones.
• Cambio los tornillos por otros más largos. = I replace the screws with longer ones.

Because otros refers to tornillos, it is masculine plural.

Because más largos agrees with the implied noun tornillos, which is masculine plural.

• tornillo = masculine singular
• tornillos = masculine plural

So the adjective must match:

• un tornillo más largo = a longer screw
• unos tornillos más largos = some longer screws

Even though tornillos is not repeated after otros, it is still understood:

• otros más largos = other ones that are longer

Yes, but it would mean something slightly different in emphasis.

• por otros más largos = for other/ different ones that are longer
• por unos más largos = for some longer ones

Both are possible, but otros highlights the idea of replacement more clearly: you remove one set and put in a different set.

So otros más largos is very natural here.

Y simply means and, joining two actions:

• saco el destornillador del cajón
• cambio los tornillos por otros más largos

Spanish word order here is straightforward and natural:

1. time expression: Al final
2. first action: saco el destornillador del cajón
3. second action: y cambio los tornillos por otros más largos

You could move al final to another position, but the original order is the most natural:

• Saco al final el destornillador... sounds less natural here.

Yes. Destornillador is the standard word for screwdriver in Spain and across the Spanish-speaking world.

It comes from:

• des-
• tornillo = screw

So it is literally something like unscrewer, though in real use it just means screwdriver.

Related words:

• tornillo = screw
• atornillar = to screw in
• desatornillar = to unscrew

A natural past version would be:

• Al final saqué el destornillador del cajón y cambié los tornillos por otros más largos.

Changes:

• saco → saqué
• cambio → cambié

This is the preterite, used for completed actions in the past.

So:

• saco / cambio = present
• saqué / cambié = I took out / I changed

This is a very useful comparison if you are learning how Spanish narrates actions.