One, without axial guidance

Structural features bearing code
RSTO no outer wall, a cage, curved Roller bearing surface
RSTO .. ​​X sealed, no inner cylindrical roller surface
STO no outer wall, a cage, curved rolling surface
STO .. ​​X double sealed, no inner cylindrical roller surface
RNA22 .. 2RS outer pairs of ribs, with cage, curved rolling surface
RNA22 .. 2RS X double sealed inner cylindrical rolling surface
NA22 .. 2RS outer pairs of ribs, with roll cage curved surfaces
NA22 .. 2RS X double sealed inner cylindrical rolling surface