61904-ZZ 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 61904-ZZ model number is decoded

61904-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 thin 619xx section (diameter series 9 of ISO 15), multiplying bore code 04 by five gives the 20 mm bore; the 37 mm outside diameter and 9 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 20 mm shaft under normal load, catalogue practice seats it on a k5 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. NSK catalogue order number: 6904ZZ (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

• At a 20 mm bore, a shaft-seat burr or an overtight setscrew can score the thin inner ring of 61904-ZZ; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
• The 619xx thin section (8.5 mm section height at 20 mm bore) trades load capacity for compactness; stiff, accurately aligned seats are essential or edge loading will spall the raceway early.
• ZZ shields are non-contact: 61904-ZZ blocks chips and coarse dust but is not waterproof — do not install it expecting a pressure-wash seal, step up to 61904-2RS for that.
• Do not wash 61904-ZZ in solvent before mounting: the grease inside the shielded cavity is the service fill, and solvent creeping past the shield gap strips it out.
• Grease compatibility is not guaranteed between fills: mixing lithium and polyurea thickeners in a 61900-series position can soften the mixture and leak — clean out the old fill before switching grease types.
• Shaft and housing fillets must clear the bearing chamfer so the 9 mm-wide ring seats square; provide an undercut or withdrawal groove instead of relying on an oversized radius.
• NSK catalogues the shielded version as 6904ZZ — 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.
• The 20 mm bore puts 61904 in NSK's light industrial range; the standard pressed-steel cage and CN clearance cover most fractional-horsepower motor and small-pump duty. NSK's VV non-contact seal is the high-speed choice here — DDU contact seal costs roughly 30–40% of the open-bearing speed ceiling.
• NSK rates 61904 at 7 kN dynamic (C) and 3.7 kN static (C0); this light-to-medium rating suits fractional-horsepower drives and instruments — for conveying or gearbox duty with shock loads, verify the equivalent dynamic load stays well below C.
• At only 37 g, 61904 is a lightweight NSK bearing that can be handled by hand; still, press it onto the shaft with a sleeve against the inner ring — never through the balls or outer ring.
• The 20×37×9 mm envelope of 61904 gives a D/d ratio of 1.85 and 8.5 mm radial section height — a standard NSK medium section that balances load capacity and speed; for this geometry the pressed-steel cage is adequate up to NSK's listed speed ratings, and C3 clearance is the common choice for hot shafts.
• The 7/3.7 kN load ratings, mass 37 g here are NSK Rolling Bearings E1103 Part C catalogue figures for 6904ZZ on the 20×37×9 mm ISO 15 envelope; internal geometry and ratings legitimately differ between brands, so re-verify before substituting another manufacturer's 61904 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 61904; in motor duty where heat build-up matters, VV is the usual compromise between debris protection and speed capability.