Подвес и крепление проверены.

Because подвес и крепление is a compound subject: two things joined by и (and). In Russian, that makes the predicate plural.

• подвес = singular
• крепление = singular
• together = plural idea

So Russian uses проверены (checked) in the plural.

If there were only one item, you would get singular:

• Подвес проверен.
• Крепление проверено.

They are in the nominative case.

That is because they are the things being talked about as the subject of the sentence: the suspension and the fastening/mounting are checked.

You can tell they are in their basic dictionary forms:

• подвес
• крепление

Проверены is a short-form passive participle from the verb проверить (to check, to inspect).

In sentences like this, it functions as the predicate and often means something like:

• have been checked
• were checked
• are checked (in a resultative sense)

This kind of form is very common in technical, official, and written Russian.

Russian often does not need a separate verb like English were or have been in this kind of sentence.

So:

• Подвес и крепление проверены.

is a normal compact Russian way to say that the items are in the state of having been checked.

A fuller version is also possible:

• Подвес и крепление были проверены.

That sounds more explicitly like were checked, but the shorter version is very common, especially in reports, manuals, inspection notes, and labels.

Because those would be singular forms, and this sentence has two nouns joined by и.

Compare:

• Подвес проверен. — masculine singular
• Крепление проверено. — neuter singular
• Подвес и крепление проверены. — plural

So the plural form is required.

• подвес is masculine
• крепление is neuter

Why?

• A noun ending in a consonant like подвес is usually masculine.
• A noun ending in -ие like крепление is neuter.

This matters in singular agreement:

• Подвес проверен.
• Крепление проверено.

But in your sentence, since both nouns are together, Russian uses the plural проверены.

Yes, it is a complete sentence.

In Russian, a short-form passive participle like проверены can serve as the predicate by itself. So nothing is missing grammatically.

This is especially normal in concise styles such as:

• technical writing
• inspection checklists
• maintenance reports
• official notes

So the sentence is short, but fully correct.

Yes. It presents the checking as a completed result.

That is because it comes from проверить, which is a perfective verb. Perfective verbs in Russian usually focus on completion or result.

So проверены implies something like:

• the inspection has been completed
• the items stand in the state of having been checked

No, Russian word order is fairly flexible.

The version you have:

• Подвес и крепление проверены.

is neutral and natural.

You could also say:

• Проверены подвес и крепление.

That puts a little more focus on the result checked.

Both are grammatical, but the original order is very normal for straightforward reporting.

Because the sentence is talking about one suspension/hanger item and one fastening/mounting item as parts of some object or assembly.

Russian often names components in the singular when referring to them as individual parts of a system.

If there were several of each, you would use plurals, for example:

• Подвесы и крепления проверены.

So the singular here does not mean the sentence is wrong; it just means the context is probably about one of each part.

Yes. The exact English depends on the context, especially because Russian does not use articles like a or the.

Possible translations include:

• The suspension and fastening have been checked.
• The hanger and mounting have been checked.
• The suspension and attachment were checked.

The best English wording depends on what подвес and крепление refer to in the technical context.