NTNDouble-Row Self-Aligning Ball Bearing – 40 mm Cylindrical Bore, 90 mm OD, 33 mm Width, Open, C3 Clearance, Pressed Steel Cage, 2 Pcs

Product Description

What this part is

NTN 2308C3 is a double-row self-aligning ball bearing with a cylindrical bore, 40 mm bore by 90 mm outside diameter by 33 mm width. Two rows of balls run on a common spherical raceway ground into the outer ring, so the inner ring and ball complement swivel freely inside the outer ring.

Decoding the designation

The 23 gives the self-aligning double-row dimension series and 08 is the bore code, 08 × 5 = 40 mm. The absence of a K suffix means the bore is cylindrical and mounts directly on the shaft journal. C3 denotes radial internal clearance greater than normal.

What these specs mean in practice

The spherical outer raceway absorbs angular error between shaft and housing, so a self-aligning ball bearing tolerates shaft deflection and imperfectly bored housings that would preload a deep groove bearing. That geometry also means the outer ring exerts almost no restoring moment. Basic load ratings are 45.5 kN dynamic and 13.5 kN static — the low static figure relative to the dynamic figure is characteristic of the two-row self-aligning geometry, where contact between ball and spherical outer raceway is comparatively shallow.

Internal clearance

C3 opens the running clearance beyond the CN standard. Extra clearance absorbs the loss of clearance caused by a heavy interference fit on the shaft and by a temperature difference between inner and outer rings, so it suits hot running and tight shaft fits. Calculation factors from the NTN catalogue are Y1 1.50, Y2 2.30 and Y0 1.50.

Quantity and configuration

Two bearings, open on both faces, cylindrical bore, pressed steel cage, C3 clearance. Mass 0.890 kg each.

Mounting data

Shaft shoulder diameter da 48 mm minimum, housing shoulder Da 82 mm maximum, ring corner radius r 1.5 mm with a permissible fillet ras of 1.5 mm. Limiting speed is 6,300 rpm on grease and 8,000 rpm on oil. Operating temperature range −40 to 120 °C. Open faces take either grease or circulating oil.

Interchange guidance

SKF 2308 E-2RS1TN9/C3 (contact seals both sides) and FAG 2308-TVH-C3 are C3 self-aligning ball bearings in the 40 x 90 x 33 mm size; both use a glass-fibre polyamide cage in place of the NTN pressed steel one, and the published ratings move with the cage. NTN 2308 is the same geometry in CN clearance and NTN 2308K is the 1:12 tapered-bore version for adapter sleeve mounting — both are related sizes rather than substitutes.