6321-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-NSK model number is decoded

In the 6300-series (diameter series 3 of ISO 15) the last two digits encode the bore: 6321 carries bore code 21 = 105 mm. Outside diameter 225 mm and width 49 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 105 mm shaft, typical catalogue practice is a m6 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. In the NSK catalogue this open execution carries the bare designation; protected variants are ordered separately with suffixes ZZ (steel shields), VV (non-contact rubber seals) and DDU (contact rubber seals).

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 series gains rating at 105 mm bore through a 225 mm OD and 49 mm width; the heavier rolling elements also trade away some speed versus a 6221.
• Storage matters for open bearings: 6321-NSK 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 6300-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6321 units.
• The housing bore for the 225 mm OD should be round within IT7; an oval bore pinches the outer ring of 6321-NSK and shows up later as two-point loaded raceway wear.
• Measure the shaft, do not trust the drawing: a 105 mm nominal journal worn by even 0.02 mm turns an interference seat into a creeping fit that frets the bore of 6321-NSK.
• The open 6321 has no integral sealing; in the NSK E1103 catalogue the protected variants carry suffixes ZZ (non-contact steel shields), VV (non-contact rubber seals) and DDU (contact rubber seals). NSK does not offer a low-torque contact seal equivalent to NTN's LLH in this catalogue — for high-speed sealed duty specify the VV non-contact seal and an external housing labyrinth.
• 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 6321 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.
• 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.
• 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.