6308-2RS-NTN bearing: complete specifications & equivalents

Specification table

Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203-3/E (2024)) · extracted 2026-09-25

Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203-3/E (2024)); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.

Cross references & equivalents

Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.

How the 6308-2RS-NTN model number is decoded

In the 6300-series (diameter series 3 of ISO 15) the last two digits encode the bore: 6308 carries bore code 08 = 40 mm. Outside diameter 90 mm and width 23 mm come from the ISO 15 boundary-dimensions general plan. Suffix -2RS denotes two contact-type elastomer seals over a lifetime grease fill; the sealing lips add drag compared with open or shielded versions. For normal-load mounting with a rotating inner ring on a 40 mm shaft, typical catalogue practice is a k5 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. NTN's contact-seal catalogue number is 6308LLU (suffix LLU, or LLH low-torque variant), mapped here from the industry-neutral -2RS spelling; the contacting lip lowers the speed ceiling versus the open bearing.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• At a 40 mm bore, a shaft-seat burr or an overtight setscrew can score the thin inner ring of 6308-2RS-NTN; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
• The 63xx medium series gains rating at 40 mm bore through a 90 mm OD and 23 mm width; the heavier rolling elements also trade away some speed versus a 6208.
• Heat is the enemy of the sealed 6308-2RS: sustained running near the lip temperature limit hardens the rubber, after which grease escapes and dirt tracks in — watch the housing temperature in hot drives.
• Never wash a sealed 6308-2RS-NTN in solvent or press it home via the outer ring; solvent destroys the grease thickener and mounting force through the seal deforms the lip.
• A 40 mm bore listing showing the right d/D/B but no standard or precision-class reference may be a loose-tolerance import; measure bore/OD spread before fitting it to a machined shaft.
• Do not quieten a noisy bearing by preloading it: the 6300-series is a deep-groove design, not angular-contact; axial preload raises temperature and shortens grease life.
• NTN catalogues the contact-sealed version as 6308LLU (suffix LLU), mapped here from the industry-neutral -2RS spelling; it is greased for life and the contacting lip lowers the speed ceiling versus the open bearing.
• The 40 mm bore puts 6308 in NTN's general-purpose industrial range; the standard pressed-steel cage and CN clearance cover most electric-motor and pump duty, but for continuous high-speed use specify the LLH low-torque seal (not LLU) and confirm the housing allows the listed limiting speed.
• At 5300 r/min the grease limiting speed for 6308 covers medium-duty industrial drives; the contact seal (LLU) is the main speed limiter here — for continuous operation above 80% of this figure use the open variant with an external labyrinth seal and oil bath.
• NTN rates 6308 at 45 kN dynamic (C) and 24 kN static (C0), 1.83 kN fatigue load limit Cu; this upper-medium rating covers conveyor and gearbox drives, but at these loads the pressed-steel cage can be the limiting factor under shock — consider the machined brass cage (suffix M) for impact duty.
• At 630 g, 6308 requires a soft-jaw vise or arbor press for mounting — never hammer it onto the shaft, and support the opposite ring to avoid brinelling the raceways.
• The 40×90×23 mm envelope of 6308 gives a D/d ratio of 2.25 and 25.0 mm radial section height — a heavy section built for high-load, lower-speed duty; specifying it in a high-rpm motor generates excess heat and shortens grease life, so prefer a 62/63-series there.
• The 45/24 kN load ratings, 1.83 kN fatigue load limit Cu NTN lists the grease limiting speed at 5300 r/min for this designation; oil-mist or jet lubrication raises the ceiling but requires a sealed-housing review. and 630 g mass here are NTN Ball and Roller Bearings CAT.No.2203-3/E figures for 6308LLU on the 40×90×23 mm ISO 15 envelope; internal geometry and ratings legitimately differ between brands, so re-verify before substituting another manufacturer's 6308 in a rated drive.
• Two NTN bearings of the same designation from different production lots can carry minor internal-geometry revisions; for paired or preloaded arrangements on one shaft, order a single lot through the NTN distributor.
• Order the C3 internal-clearance version (6308 with C3 after the seal code) when the shaft fit is tight or the shaft-to-housing temperature gradient exceeds roughly 10 °C — the residual clearance after mounting, not the catalogue CN figure, decides service life.