SNR7204HG1DUJ84Super Precision Angular Contact Bearing Pair 20x47x14 mm 25° Duplex Universally Ground

Product Description

What this part is

SNR 7204HG1DUJ84 super-precision single-row angular contact ball bearings, supplied as a universally ground duplex pair. Brand: SNR (now NTN-SNR). Series: 72. Base Number: 7204. Bore: 20 mm (0.7874 in). Outside Diameter: 47 mm (1.8504 in). Width: 14 mm (0.5512 in) per bearing. Total Width: 28 mm as a duplex pair. Contact Angle: 25°. Precision Class: ISO 4, P4, ABEC 7. Preload: Medium, 92 lbf. Dynamic Load Rating: 15.04 kN (3,380 lbf) per bearing. Static Load Rating: 8.50 kN (1,910 lbf) per bearing. Limiting Speed: 28,000 rpm on grease, 43,000 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. Item weight: 0.24 lbs. Unit Quantity: 2 Pcs, one matched duplex set.

Decoding the designation

72: the 72 dimension series, the heavier of the two SNR high-precision sections. 04: 20 mm bore code. H: 25° contact angle. G1: the high-load-capacity version of the 72 series, the section built to carry predominantly high axial loads. 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. 8: medium preload. 4: precision class ISO 4, ABEC 7, P4. Searchable forms: 7204HG1DUJ84, 7204 H G1 DU J84, 7204-H-G1-DU-J84, 7204.H.G1.DU.J84, and the world equivalent 7204-E-T-DUM-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. The 72 series carries a heavier section than the 70 and 719 sections on the same bore, which is what lifts the load ratings. Medium preload sits between the light grade chosen for speed and the heavy grade chosen for maximum rigidity, giving spindle stiffness without the thermal penalty of the heavy grade. 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: 28,000 rpm on grease and 43,000 rpm on oil, both figures for a single bearing. Speed changes when bearings are matched into an arrangement. A back-to-back pair at medium preload runs at 0.70 of the single-bearing figure, giving 19,600 rpm on grease and 30,100 rpm on oil. A face-to-face pair at medium preload runs at 0.65, giving 18,200 rpm on grease and 27,950 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 medium 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.

Interchange guidance

Same-envelope 20 x 47 x 14 mm, 25°, P4 universally ground alternatives at medium preload: FAG / Schaeffler 7204-E-T-P4-DUM, NSK 7204A5TYNDUMP4, SKF 7204 ACD/P4ADGB, and Timken Fafnir 3MM204WI-DUM. In the SKF scheme DGB is the medium preload grade, and in the NSK scheme A5 is the 25° angle. Preload class matches within a single spindle stack, and this set is the medium grade. A 15° execution, coded C in the SNR and NSK schemes, is a related size rather than an interchange, since contact angle changes both axial stiffness and the load ratings.