The RNA6904UU is a Standard Duty . Single Row Machined Needle Roller Bearing with an oil groove . an oil hole in the Outer Ring . and 2 Rubber Seals. This Bearing has no Inner Ring . meaning the Needle Rollers are mounted directly onto the shaft. As such . the Bearing has better running accuracy as it isn't affected by assembling an Inner Ring with the shaft. In caged Needle Roller Bearings like this one . the Needles are precisely guided by the Cage to achieve ideal load distribution. These Bearings are designed for high load carrying capacity in radially compact arrangements and are used in most general purpose applications. The Bearing's dimensions are 25X37X30mm.