6408-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 6408-NTN model number is decoded

In the 6400-series (diameter series 4 of ISO 15) the last two digits encode the bore: 6408 carries bore code 08 = 40 mm. Outside diameter 110 mm and width 27 mm come from the ISO 15 boundary-dimensions general plan. With no seal suffix the bearing is open: no shields or seals are fitted and lubrication is supplied by the application. 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. In the NTN catalogue this open execution carries the bare designation; protected variants are ordered separately with suffixes ZZ (shields), LLB/LLF (non-contact seals), LLH (low-torque contact seal) and LLU (contact seal).

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 6408-NTN; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
• The 64xx heavy section at 40 mm bore exists for high radial load at moderate rpm; its 110 mm OD and 27 mm width demand a larger housing, and grease life at motor speeds is short — treat it as a low-speed, high-load choice.
• Storage matters for open bearings: 6408-NTN leaves the factory with rust preventive only, so clean it and apply the service grease at assembly even if the rings look oily from the wrapper.
• Open bearings tolerate the highest speeds in the 6400-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6408 units.
• Axial location must clamp the ring face, not the seal area: a shoulder or circlip bearing on the seal side of the 27 mm-wide ring of 6408-NTN drags the lip and overheats it.
• Vibration during standstill brinells the raceways of a 40 mm bearing at ball spacing; if the machine sits idle next to running equipment, turn the shaft over periodically or isolate the arrangement.
• The open 6408 has no integral sealing; in the NTN 2203 catalogue the protected variants carry suffixes ZZ (non-contact steel shields), LLB/LLF (non-contact rubber seals), LLU (contact rubber seals) and LLH (a low-torque contact seal with higher speed capability than LLU). A JR or JRX suffix (printed for some thin-section sizes) denotes a pressed-steel cage, not a seal.
• The 40 mm bore puts 6408 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 7000 r/min the grease limiting speed for 6408 covers medium-duty industrial drives; the open or shielded execution can run continuously at this speed with standard lithium-soap grease.
• At 70.5 kN dynamic load rating (C) and 36.5 kN static (C0), 2.85 kN fatigue load limit Cu, 6408 is a heavy-load bearing for industrial gearboxes and large conveyors; NTN expects a machined brass cage (suffix M) at this rating for shock duty, and the static C0 must be checked against any mounting or lifting loads.
• At 1230 g (1.2 kg), 6408 needs mechanical handling for mounting; NTN recommends induction heating the inner ring (max 120 °C) rather than pressing cold, and a lifting eye if the housing is pre-assembled.
• The 40×110×27 mm envelope of 6408 gives a D/d ratio of 2.75 and 35.0 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 70.5/36.5 kN load ratings, 2.85 kN fatigue load limit Cu NTN lists the grease limiting speed at 7000 r/min for this designation; oil-mist or jet lubrication raises the ceiling but requires a sealed-housing review. and 1230 g mass here are NTN Ball and Roller Bearings CAT.No.2203-3/E figures for 6408 on the 40×110×27 mm ISO 15 envelope; internal geometry and ratings legitimately differ between brands, so re-verify before substituting another manufacturer's 6408 in a rated drive.
• Factory-fill grease in NTN sealed units is a general-duty lithium-soap grease; food-grade, low-temperature and high-temperature fills are request options at order time, because LLU/LLB units are not meant to be opened and re-greased in the field.
• Order the C3 internal-clearance version (6408 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.