Bearings very simular to normal grooved ball bearings. The only difference being, that on the outer diameter they have a flange. Which can be very useful for mounting the bearings in through holes or other specific apllications.
These flanges are normaly mounted on steppermotors. We often took old motors apart to use the flanges. We now have the new variant. The standard 608ZZ ballbearings fit, these are very handy in combination with the trapezium thread.