Everything in  are optional, rarcrack default crack two threads and autodetect the archive type. If the detection wrong you can specify the correct file type with the type parameter. RarCrack currently crack maximum in 12 threads.
After the cracking started RarCrack will print the current status of cracking and save it’s to a status file. If you want more specific password character set, you need to run RarCrack to create the XML status file (3 sec).