Montpáku používám na plášť.

Because montpáku is the accusative singular form of montpáka.

The verb používat / používat něco means to use something, so its direct object goes in the accusative case.
Here:

• montpáka = nominative singular
• montpáku = accusative singular

So Montpáku používám... literally has tire lever as the object: I use the tire lever...

Používám means I use / I am using, depending on context.

It is:

• 1st person singular
• present tense
• from the verb používat = to use

The ending -ám often marks I in this type of verb.

Because Czech present tense can sometimes cover meanings that English splits into I use and I’m using, context decides which is more natural in translation.

Here na means something like for or for use on.

So montpáku používám na plášť means that the tire lever is used for the tire.

In Czech, na has several meanings depending on context. It can mean:

• on / onto
• for
• to deal with / against
• other related uses

In this sentence, it expresses purpose or intended use:
I use the tire lever for the tire.

The case does change, but the form happens to stay the same.

After na in this meaning, plášť is in the accusative. But plášť is a masculine inanimate noun, and for many masculine inanimate nouns, the nominative and accusative singular are identical.

So:

• nominative: plášť
• accusative: plášť

The case is different grammatically, even though the word looks the same.

Yes, plášť can mean coat/cloak, but in cycling it also means the outer tire.

That is a very common thing in Czech: one word can have a general meaning and also a specialized meaning in a certain context.

So in everyday language:

• plášť = coat, cloak

In bike-related language:

• plášť = tire (more precisely the outer tire)

So the cycling context makes the meaning clear here.

Yes, it is normal, but it is not the most neutral order.

Czech word order is more flexible than English because case endings show grammatical roles. Starting with Montpáku puts extra attention on the object.

Possible orders include:

• Montpáku používám na plášť.
• Používám montpáku na plášť.

The second one may feel more neutral to many learners. The first one can sound like As for the tire lever, I use it for the tire or put emphasis on montpáku.

So the sentence is grammatical, and the choice of order affects emphasis more than basic meaning.

Because Czech has no articles.

English needs words like:

• a
• an
• the

Czech does not. Whether something is a tire lever, the tire lever, or just tire lever is understood from context.

So Montpáku používám na plášť could correspond to English with or without an article depending on the situation.

Yes, používat is perfectly natural for to use.

A related verb is použít, which is the perfective partner:

• používat = to use, to be using, to use regularly/habitually
• použít = to use once, to make use of, to employ in a completed event

So:

• Montpáku používám na plášť. = I use the tire lever for the tire / I use tire levers on tires
• Montpáku jsem použil na plášť. = I used the tire lever on the tire (completed action)

This is a common Czech aspect pair.

A Czech speaker would usually understand it as for working with the tire or for use on the tire.

With tools, Czech often uses na + accusative to express what something is intended for.

Compare the idea in English:

• a brush for shoes
• a key for the door
• a tool for tires

So montpáku ... na plášť means the tire lever is used in connection with the tire, especially when removing or fitting it.

A rough pronunciation guide is:

MONT-paa-koo POU-zhee-vaam naa plahsht

A few helpful notes:

• á is a long vowel, so pá is longer than a short a
• ž sounds like the s in measure
• š sounds like sh
• ť is a softened t
• Czech stress is usually on the first syllable of each word:
  • MONTpáku
  • POUžívám
  • na
  • PLÁŠŤ

The word montpáka is a bit colloquial and tool-specific, so hearing it from cyclists or mechanics is very normal.