Why Saat ... became Saatler and not Saatlar?
can you tell me more words same to this case?... thanks

Thanks Elisa ... So it is because importing words from Arabic ...

In fact, the reason is not because they are from Arabic. The reason is the pronunciation of the last syllable.

For example: kitap is from Arabic too, but suffixes are suitable to vowel harmony: kitaplAr

Look at "saat"s lat syllable. it is "at". normally there is another word "at" (horse). It's pronunciation has a bass voice "a". But "saat"s last syllable "at" has a treble voice as "a" like a letter between "a" and "e". So, you have to add the suffixes as if the last syllable is "e".

Teşekkurlar Caliptrix ...
That is making more sense and it is a contirbution to this topic.