Seřídím sedlo imbusovým klíčem.

Because seřídit is a perfective verb. In Czech, perfective verbs normally do not express a present ongoing action. Their present-tense forms usually refer to the future.

So:

• seřídím = I will adjust / I’ll tune
• not I am adjusting

This is very common in Czech:

• udělám = I will do
• napíšu = I will write
• opravím = I will fix

If you want I am adjusting, Czech would usually use the imperfective verb instead, for example seřizuji.

The dictionary form is seřídit.

This is the perfective infinitive, meaning something like to adjust, to tune, or to set correctly.

The form seřídím is:

• 1st person singular
• from seřídit
• meaning I will adjust

A few related forms:

• seřídíš = you will adjust
• seřídí = he/she/it will adjust
• seřídíme = we will adjust

Because Czech usually does not need subject pronouns when the verb ending already shows who the subject is.

In seřídím, the ending -ím tells you it means I.

So:

• Seřídím sedlo. = I’ll adjust the saddle.
• Já seřídím sedlo. = also possible, but já is added only for emphasis, contrast, or clarity.

For example:

• Já seřídím sedlo, ty opravíš brzdy.
  I’ll adjust the saddle, and you’ll fix the brakes.

Sedlo is the direct object of the verb, so it is in the accusative case.

However, sedlo is a neuter noun, and for many neuter nouns the nominative and accusative singular look the same.

So:

• nominative: sedlo
• accusative: sedlo

That is why the form does not change.

Sedlo literally means saddle. In everyday use, it can refer to the saddle/seat on things like:

• a bicycle
• a motorcycle
• a horse

In this sentence, it most naturally means a bicycle saddle/seat.

So English might translate it as either:

• saddle
• seat

depending on the context.

Because Czech uses the instrumental case to express the tool or means used to do something.

Here, imbusovým klíčem means:

• with an Allen key
• using an Allen key

So the sentence literally works like:

• I will adjust the saddle with an Allen key.

This is a very common use of the instrumental in Czech.

More examples:

• Píšu perem. = I write with a pen.
• Otevřel dveře klíčem. = He opened the door with a key.

Imbusový klíč is the common Czech term for an Allen key or hex key.

Breakdown:

• klíč = key / wrench
• imbusový = Allen / hex-type

So:

• imbusový klíč = Allen key
• instrumental singular: imbusovým klíčem

You may also hear other terms in technical contexts, but imbusový klíč is very normal everyday Czech.

Yes, but the meaning changes.

• Seřídím sedlo imbusovým klíčem.
  = I will adjust the saddle with an Allen key.
  This is perfective, so it points to a completed future action.

• Seřizuji sedlo imbusovým klíčem.
  = I am adjusting the saddle with an Allen key. / I adjust the saddle with an Allen key.
  This is imperfective, so it describes an ongoing or repeated action.

If you want the future of the imperfective verb, you would say:

• Budu seřizovat sedlo imbusovým klíčem.
  = I will be adjusting / I will adjust
  but this focuses more on the process than on completion.

No, Czech word order is fairly flexible because the cases show the grammatical roles.

Seřídím sedlo imbusovým klíčem is a natural neutral order.

But other orders are also possible, with different emphasis:

• Sedlo seřídím imbusovým klíčem.
  Emphasis on the saddle.
• Imbusovým klíčem seřídím sedlo.
  Emphasis on with an Allen key.
• Seřídím imbusovým klíčem sedlo.
  Also possible, though a bit less neutral.

So the basic meaning stays the same, but the focus shifts.

Because Czech often expresses instrument / means simply with the instrumental case alone, without a preposition.

In English, you usually need with:

• with an Allen key

In Czech, the case ending itself carries that meaning:

• imbusovým klíčem

So no extra word is necessary.

Yes, ř is one of the most famous difficult Czech sounds.

A rough pronunciation guide:

• seřídím ≈ seh-rzhee-deem, very approximately

About ř:

• it is a special Czech sound
• it is something like a rolled/trilled r combined with a zh sound
• there is no exact English equivalent

You do not need to master it immediately. Learners are often understood even if they pronounce it closer to:

• r
• or zh/r-like

Also note the long vowels:

• ří has a long í
• final -dím also has a long í

Because Czech does not have articles.

So Czech simply says:

• sedlo = the saddle, a saddle, or just saddle

and

• imbusovým klíčem = with an Allen key / with the Allen key

The exact meaning depends on context.

In this sentence, English naturally adds articles:

• I will adjust the saddle with an Allen key.

But Czech does not need separate words for the or a/an.