6321-ZZ-NSK bearing: complete specifications & equivalents

Specification table

Source: catalog reference (NSK Rolling Bearings E1103 Part C) · extracted 2026-09-24

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-ZZ-NSK model number is decoded

6321-ZZ carries two non-contact sheet-steel shields that hold the factory grease in and keep coarse debris out; they do not seal against liquids. 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. NSK catalogue order number: 6321ZZ (suffix ZZ), two non-contact steel shields, mapped here from the industry-neutral -ZZ spelling.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Mount this 105 mm bore bearing by heating the inner ring (induction heater, max 120 °C) — never drive it home through the outer ring or balls, that brinells the raceways.
• 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.
• ZZ shields are non-contact: 6321-ZZ-NSK blocks chips and coarse dust but is not waterproof — do not install it expecting a pressure-wash seal, step up to 6321-2RS for that.
• Do not wash 6321-ZZ-NSK in solvent before mounting: the grease inside the shielded cavity is the service fill, and solvent creeping past the shield gap strips it out.
• 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.
• Shaft and housing fillets must clear the bearing chamfer so the 49 mm-wide ring seats square; provide an undercut or withdrawal groove instead of relying on an oversized radius.
• NSK catalogues the shielded version as 6321ZZ — suffix ZZ, two non-contact steel shields. The industry-neutral page spelling is -ZZ; quote the NSK order number when buying through an NSK channel.
• At 105 mm bore 6321 is in NSK's medium industrial range; the pressed-steel cage is standard, but large-section 63xx 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 NSK channel if the application sees impact loads.
• NSK rates 6321 at 202 kN dynamic (C) and 154 kN static (C0); this heavy-load rating is at the upper end of the E1103 Part C single-row deep-groove extract — NSK supplies a machined brass cage (suffix M) and expects an application review, because catalogue L10 life alone does not capture shock and misalignment loads at this rating.
• At 8090 g (8.1 kg), 6321 is a heavy NSK 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 NSK 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 202/154 kN load ratings, mass 8090 g here are NSK Rolling Bearings E1103 Part C catalogue figures for 6321ZZ 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. NSK does not tabulate reference or limiting speeds in the E1103 Part C dimension tables used for this page — consult NSK's separate speed-rating tables before high-speed service.
• Keep NSK bearings in the original packaging until fitting: the wrapper carries the production lot, and the unopened shelf life of greased sealed units is typically quoted at three to five years in dry, vibration-free storage.
• NSK's VV non-contact seal keeps frictional torque close to the open 6321; in motor duty where heat build-up matters, VV is the usual compromise between debris protection and speed capability.