the bearings in your ZA50 are referred to as c3 fitment bearings. this rating refers to the "play" or tolerance that the bearing is manucfatured to...
hence a c1 fitment bearing runs extremely tight and is nat made for applications that the bearing will heat up and expand and then seize
c3 is the fitment that you have on all your internal bearings and is the most common bearing type used in almost everything made
for my peugeot 103 project i called a local bearing shop, just by using the yellow pages and asked them to make ame a hybrid ceramic bearing.
hybrid refers to the fact that the outer and inner races are still made of steel the balls are silicon nitride and the carrier is either plastic, steel or ceramic
for a high quality European made SKF or FAG steel bearing in a common type 6203 for example should cost you retail anywhere from 7-20 bucks.
the ceramic hybrids i had made for me have a 20k max RPM and about 3 times the life and half the rolling resistance of a steel bearing. they cost me about $60 a piece and it took the shop 2 weeks to get the materials and make them
i got mine from Bearing Depot
these guys are no bullshit, call them with exactly the bearing numbers that you need and the fitment you want (c3) and you wont have any issues. they wont crosss reference anything, so you just need to know what you want.
fi you guys have any more questions you can call me at my shop
732 635 0094
ask for matthew
local heroes over and out