does this help ?
http://www.grizzly.com/products/G0555/parts
the 6(000ZZ )= 6000ZZ Bearing , 6(204LLU) = 6204LLU <-- Industry Standard Bearing number.
ZZ means double shielded. You want double sealed instead. Bearing will say 2-RS, instead of ZZ. Fastenal either has it in stock, or next day for less than two bucks. I wouldn't go overboard and buy expensive bearing for this application, as it's a "wear item."