NTNNF308Cylindrical Roller Bearing 40 x 90 x 23 mm, Single Row, NF Design, One-Direction Axial Location

Product Description

What this part is

An NTN NF308 single-row cylindrical roller bearing, 40 mm bore, 90 mm outside diameter, 23 mm wide. Cylindrical rollers in line contact with the raceways give a high radial rating and high radial stiffness for the envelope. The rings are separable, and the bearing locates the shaft axially in one direction as well as carrying its radial load.

Decoding the designation

N is the cylindrical roller design with two integral guide ribs on the inner ring and a plain outer ring. F adds one integral rib to the outer ring, and that single rib is what gives the bearing axial location in one direction. 3 and 08 give the ISO 03 dimension series and the bore code, 40 mm at five millimetres per unit. No cage suffix appears, which means the pressed steel cage; no clearance suffix appears, which means CN, normal radial internal clearance.

Axial location on the cylindrical roller family

The design letters are the whole specification on this bearing type. N and NU provide no axial location and float. NF and NJ locate the shaft in one direction. NUP locates in both. NH is an NJ plus a separate HJ angle ring. The N-family and NU-family differ in which ring carries the ribs: on an N or NF the ribs are on the inner ring, on an NU or NJ they are on the outer. That determines which ring is separable and which way round the bearing goes into the housing.

What these specs mean in practice

A one-direction locating cylindrical roller earns its place where the shaft carries thrust in a single known sense — a helical gear pinion or a fan impeller — and where a floating bearing elsewhere on the shaft absorbs thermal growth. The single rib takes light to moderate thrust intermittently; sustained heavy thrust belongs on a thrust or angular contact bearing. The pressed steel cage suits moderate speeds, and a machined brass cage is the path where speed, temperature or shock rise.

Quantity and configuration

1 Pc, comprising the ribbed inner ring with its roller and cage assembly plus the matching one-ribbed outer ring. Open both faces, no seals or shields. No HJ angle ring.

Fitting notes

The rings mount separately and are then brought together axially, with the outer-ring rib oriented to face the thrust it has to react. Line contact makes the type sensitive to misalignment, so the shaft seat and housing bore want to be concentric and square. Roller sets stay with their own inner ring, since the two are matched at manufacture.

Interchange guidance

The ISO base number is NF308, so another maker’s NF308 or NF308E with a pressed steel or brass cage is a genuine interchange on fit and axial behaviour. N308 is a related size, not a substitution, because it has no outer-ring rib and provides no axial location. NU308 and NJ308 fit the same 40 x 90 x 23 seat but carry their ribs on the opposite ring, and NUP308 locates in both directions — all different parts.