So i did a little research on 6204 bearings.
There are a lot of different types from different manufactureres out there. So i needed to know more details and found a very good introduction on roller bearings from NSK. Maybe it is also available in english, but i couldn't find.
http://www.tmh-at.de/downloads/files/nsk/Hauptkatalog_-_Waelzlager_-_PDF_-_Teil_A.pdf
http://www.tmh-at.de/downloads/files/nsk/Hauptkatalog_-_Waelzlager_-_PDF_-_Teil_B.pdf
http://www.tmh-at.de/downloads/files/nsk/Hauptkatalog_-_Waelzlager_-_PDF_-_Teil_C.pdf
English infos i found (not the same as above):
Rolling Bearing Catalog Technical Information | NSK
Regards Markus