6321-2RS-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 6321-2RS-NTN model number is decoded

6321-2RS is closed by two contacting elastomer lips over a lifetime grease fill; the lips add friction, so the speed ceiling sits below the open execution. Within the medium 63xx section (diameter series 3 of ISO 15), multiplying bore code 21 by five gives the 105 mm bore; the 225 mm outside diameter and 49 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 105 mm shaft under normal load, catalogue practice seats it on a m6 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. NTN's contact-seal catalogue number is 6321LLU (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 105 mm bore the ring mass is significant: heat 6321 on an induction heater (max 120 °C), never over an open flame, and plan puller access or a withdrawal sleeve now for the day it has to come off again.
• The 63xx medium section at 105 mm bore gains dynamic rating through larger rolling elements on a 225 mm OD; the penalty is mass and a lower limiting speed than the 6221 — do not specify it for speed-critical shafts.
• Heat is the enemy of the sealed 6321-2RS: 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 6321-2RS-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 105 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.
• Axial location must clamp the ring face, not the seal area: a shoulder or circlip bearing on the seal side of the 49 mm-wide ring of 6321-2RS-NTN drags the lip and overheats it.
• NTN catalogues the contact-sealed version as 6321LLU (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.
• At 105 mm bore 6321 is in NTN's medium industrial range; the pressed-steel cage is standard but large-section 63xx/64xx sizes at this bore can be ordered with a machined brass cage (suffix M) for heavy-shock or very-low-speed duty — confirm cage material with the NTN channel if the application sees impact loads.
• NTN lists the grease limiting speed at 2100 r/min for 6321; this is a large or heavy-section size where centrifugal force and cage inertia cap the speed — for higher shaft speeds either step to a smaller bearing on the same bore or consult NTN for an oil-lubricated, machined-cage variant.
• At 204 kN dynamic load rating (C) and 153 kN static (C0), 9.35 kN fatigue load limit Cu, 6321 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 8050 g (8.1 kg), 6321 is a heavy bearing that requires a crane or hoist for handling; induction-heat the inner ring (max 120 °C) and use a mechanical puller for removal — never apply heat directly to the balls or cage.
• The 105×225×49 mm envelope of 6321 gives a D/d ratio of 2.14 and 60.0 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 204/153 kN load ratings, 9.35 kN fatigue load limit Cu NTN lists the grease limiting speed at 2100 r/min for this designation; oil-mist or jet lubrication raises the ceiling but requires a sealed-housing review. and 8050 g mass here are NTN Ball and Roller Bearings CAT.No.2203-3/E figures for 6321LLU on the 105×225×49 mm ISO 15 envelope; internal geometry and ratings legitimately differ between brands, so re-verify before substituting another manufacturer's 6321 in a rated drive.
• NTN's pressed-steel cage (no cage suffix) is the quiet standard for this size; for sustained running close to the limiting speed or for heavy shock duty, ask the NTN channel whether a machined-cage execution of 6321 is listed.
• 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.