SNR71904HVDUJ74Super-Precision Angular Contact Ball Bearing Pair 20 x 37 x 9 mm, 25° Contact Angle, P4, Light Preload, Duplex Universal

Product Description

What this part is

SNR 71904HVDUJ74 super-precision single-row angular contact ball bearings, supplied as a universally ground duplex pair. Brand: SNR (now NTN-SNR). Series: 719. Base Number: 7904. Bore: 20 mm (0.7874 in). Outside Diameter: 37 mm (1.4567 in). Width: 9 mm (0.3543 in) per bearing. Total Width: 18 mm (0.7087 in) as a duplex pair. Contact Angle: 25°. Precision Class: ISO 4, P4, ABEC 7. Preload: Light, 12 lbf. Dynamic Load Rating: 7.29 kN (1,640 lbf) per bearing. Static Load Rating: 4.67 kN (1,050 lbf) per bearing. Limiting Speed: 37,000 rpm on grease, 57,000 rpm on oil, per single bearing. Cage Material: laminated phenolic resin. Cage Type: machined, centred on the outer ring. Bearing Material: 52100 vacuum-degassed steel rings and balls. Rolling Elements: steel balls. Bore Type: straight. Closure Type: open, both faces. Number Of Rows: 1 per bearing. Internal Clearance: N/A — the set is preloaded rather than clearance-set. Unit Quantity: 2 Pcs, one matched duplex set.

Decoding the designation

719: extremely light dimension series. 04: 20 mm bore code. H: 25° contact angle. V: the high-performance version of the 719 and 70 series, built with a laminated phenolic cage centred on the outer ring. DU: a pair of universal bearings, selected so that bore and outside-diameter variation across the set stays within half the ISO tolerance. J: the character preceding the preload and precision codes. 7: light preload. 4: precision class ISO 4, ABEC 7, P4. Searchable forms: 71904HVDUJ74, 71904 HV DU J74, 71904-H-V-DU-J74, 71904.HV.DU.J74, and the world equivalent 7904-E-T-DUL-P4.

What these specs mean in practice

A 25° contact angle tilts the load path further toward the bearing axis than a 15° angle, giving higher thrust capacity and higher axial stiffness, so a spindle holds size better under heavier and interrupted cuts. The trade is speed: the steeper angle raises centrifugal and gyroscopic ball loading, so heat generation is higher than an otherwise identical 15° bearing. Light preload favours speed and thermal headroom over axial stiffness, which is why it is the grade chosen for high-rpm spindles. Laminated phenolic is light, self-lubricating and tolerant of marginal lubrication, and its low mass reduces cage loading at speed. Rings and balls are 52100 vacuum-degassed steel, a high-carbon chrome bearing steel. ISO 4 gives tighter running accuracy and lower running vibration than standard tolerance, and most SNR ISO 4 bearings achieve ISO 2 run-out accuracy.

Speed ratings

Limiting Speed: 37,000 rpm on grease and 57,000 rpm on oil, both figures for a single bearing. Speed changes when bearings are matched into an arrangement. A back-to-back pair at light preload runs at 0.80 of the single-bearing figure, giving 29,600 rpm on grease and 45,600 rpm on oil. A face-to-face pair at light preload runs at 0.75, giving 27,750 rpm on grease and 42,750 rpm on oil.

Quantity and configuration

Unit Quantity: 2 Pcs — one matched duplex universal set. Universal grinding leaves the inner and outer ring faces flush once preloaded, so any two bearings of this designation pair in any orientation and come up to the intended light preload when clamped, with no ground spacers and no matched-set paperwork. The pair mounts back-to-back (DB) for maximum moment stiffness and two-direction thrust, face-to-face (DF) for tolerance of shaft-to-housing misalignment, or in tandem (DT) to double thrust capacity in one direction.

Fitting notes

Shaft and housing seats are ground and held to super-precision tolerance, since the running accuracy of the bearing is realised on seats held to it. The etched high-shoulder faces of the two outer rings identify the arrangement and are oriented to the intended back-to-back, face-to-face or tandem stacking. Mounting is by controlled press or induction heat on the ring being fitted, with load passing through the rings rather than the ball complement. Preservative is cleaned off and the bearings lubricated to spindle specification before assembly.

Interchange guidance

Same-envelope 20 x 37 x 9 mm, 25°, P4 universally ground alternatives: SKF 71904 ACD/P4ADGA, NSK 7904A5TRDULP4, FAG / Schaeffler B71904-E-T-P4S-DUL, RHP 7904ETDULP4, and Timken Fafnir 3MM9304WI-DUL, in which the 9300 prefix maps to the ISO 719 series and 3MM marks the 25° angle. Preload class matches within a single spindle stack, and this set is the light grade. A 15° execution such as an SKF 71904 CD, FAG B71904-C or NSK 7904C is a related size rather than an interchange, since contact angle changes both axial stiffness and the load ratings.