Learn Farsi: قرقره‌ای را که خریدند، نصب کردیم. - We installed the pulley that they bought.

In standard Farsi, when a noun modified by a relative clause is the direct object of the main verb (here, we installed the pulley), the object marker râ attaches directly to that noun and its restrictive -i suffix, coming right before ke.

If the suffix -i often means 'a' or 'an', why does the translation say 'the pulley'?

The -i suffix here is not the indefinite article. It is a restrictive marker used to signal that a defining relative clause is attached to the noun. It points specifically to the pulley that they bought. Because it specifies exactly which pulley is meant, it is logically definite and translated with 'the' in English.

Why is there an Alef (ا) in قرقره‌ای before the ی?

The word for pulley, قرقره (gherghere), ends in a silent ه, which represents the short vowel 'e'. When adding the -i suffix to a word ending in a vowel, Farsi requires a phonetic bridge to separate the sounds. In modern spelling, this bridge is written with an Alef, resulting in قرقره‌ای.

In everyday speech, could I put the object marker after the whole relative clause instead?

Yes. While this sentence shows the standard written syntax, in colloquial spoken Farsi people often treat the noun and its relative clause as one big phrase block. They move the object marker (usually pronounced as ro) to the very end of that block, saying gherghere-i ke kharidand ro nasb kardim.