The Timken NU Series is a single-row cylindrical roller bearing with two integral guide ribs on the inner ring and a smooth, rib-free outer ring. That construction gives the NU two defining traits: very high radial load capacity for its envelope, and zero axial (thrust) capacity — the outer ring is free to float along the shaft axis. In a typical two-bearing shaft, the NU is the non-locating end, paired with a locating bearing (deep-groove ball, angular contact, or NUP/NJ cylindrical) that takes the axial load and absorbs shaft thermal growth without binding.

• Construction: Single-row, line-contact rollers on a cylindrical inner-ring raceway between two fixed ribs; outer ring raceway is flat and unflanged — outer ring slides freely in its housing bore.
• Load profile: Heavy pure radial only. Roller-to-raceway line contact gives significantly higher radial rating than a same-bore ball bearing; axial load is zero (any thrust must go to another bearing in the shaft system).
• Cage options: EJ / EM = pressed-steel window cage (standard through medium sizes); MA / EMA = machined brass cage (large sizes, high-speed, and shock-service applications); M = machined brass.
• Internal clearance: C0 (standard), C3 (greater than normal), C4, C5, C6 available — specify C3 or C4 for interference-fit mounting, elevated operating temperature, or heavy thermal gradients across the shaft.
• Lubrication features: W33 = oil groove and three lubrication holes on the outer ring; W49/W73/W102 codes indicate additional application-specific feature packs such as spark-erosion-resistant cages, special heat treatments, or enhanced sealing.
• Dimension series: NU 2, NU 3, NU 10, NU 22, NU 23, NU 28, NU 29, NU 30, NU 31, NU 32 — the dimension series determines the cross-section (envelope) relative to bore. NU 2 and NU 22 are the light-through-medium workhorses; NU 3 and NU 23 step up radial capacity in the same bore; NU 10 and NU 18/29/31 series cover very large bores (500 mm+).
• Typical applications: Electric motors (non-drive end), gearbox intermediate shafts, pumps and compressors, traction motors and rail drivetrains, machine-tool spindles, paper-machine dryers, rolling mills, large fans, and any shaft where thermal expansion must be accommodated.

About the NU 3 Series: Medium-series cross-section — steps up radial capacity at the same bore versus the 2 series. Common on gearboxes, traction motors, blowers, and heavy-duty pump shafts.

NU vs. NJ vs. NUP: The NJ adds one rib to the outer ring — can carry axial load in one direction (used where axial is modest and unidirectional). The NUP adds a rib plus a loose thrust collar — carries axial in both directions but with lower capacity than a dedicated thrust bearing. Choose NU when the other bearing in the shaft system handles axial and you need the free-floating outer ring to absorb thermal growth.