Green Bearings w/ Snap Ring?

[blackace]

I was looking at green bearings and saw the Moser sells them with or with the snap ring. Might be a stupid question but what is the snap ring and do I need it?

 

[70Duster440]

Basically, there are two types of greens. One has the axle retainer built into the bearing assembly and the other uses a separate retainer with a snap ring on the bearing. The retainer sandwiches the snap ring between it and the housing (the brake backing plate actually) to keep the bearing/axle in place - the axle can't be pushed in too far or come out.

If you visit my site and click on the "Chassis" link (then scroll down) you'll see pictures of this type and how it works. I believe the latter type is also preferred.