NDHQ30210DTL7AMatched Tandem Set, Angular Contact Ball Bearings 50 x 90 x 20 mm, 40 Degree Contact Angle, ABEC 7, Quiet Grade, Open, 2 Pcs

Product Description

What this part is

A matched tandem set of two New Departure Hyatt angular contact ball bearings in the 7210 envelope — 50 mm bore, 90 mm outside diameter, 20 mm width per bearing. Open, 40° contact angle, ABEC 7 precision to NDH’s quiet-running selection. The pair is ground together as one set to sit side by side facing the same way. New old stock American product, and about as much single-direction thrust capacity as you can get from ball bearings in this envelope.

Decoding the designation

30210 — NDH’s number for the ISO 7210 size, 50 x 90 x 20 mm. The 30-series prefix is the 40° angular contact family — the equivalent of a 7210B — where the 20-series is the shallower 15° build.
Q — NDH quiet-running selected series, screened for low noise and vibration.
DT — duplex tandem. Two separate single-row bearings ground as a matched set to be mounted facing the same direction. Not a double-row bearing.
L7 — NDH tolerance grade, equivalent to ABEC 7.
A — NDH internal variant suffix, carried for identification.

What these specs mean in practice

This is the high-thrust combination. A 40° contact angle points the ball load close to the shaft axis, so thrust capacity and axial stiffness are far higher than a 15° spindle bearing of the same size will manage; mounting two in tandem then roughly doubles that again, because both bearings face the same way and share the load. The cost is twofold. Speed drops, because a steep angle works the balls harder against centrifugal effects and generates more heat; and the capacity is one-directional, so the shaft still needs something opposing at the other end. Choose this arrangement for worm drives, screw jacks, extruder and press screws, vertical shafts and any position where a large axial load pushes reliably one way. ABEC 7 running accuracy is genuinely tight, so the shaft and housing seats must be ground and true to match or the grade is wasted, and the Q quiet-running selection keeps noise and transmitted vibration low on top of that.

Quantity and configuration

2 Pcs — a matched tandem set of two bearings, ground together and shipping together. Not two independent bearings; splitting the set loses the matching.

Fitting notes

Both bearings go in facing the same direction, wide land of each outer ring toward the thrust. Fitting one reversed turns the set into a back-to-back pair with entirely different load behaviour and none of the shared thrust capacity. Look for the grinding marks across the ring faces, usually a scribed line or V, and line them up on assembly — that is the orientation the set was ground in. Seats must be clean, ground and burr-free; interference fit adds to whatever preload the set carries, so check sizes against the drawing. Induction-heat rather than hammer a 50 mm bore onto a tight shaft, and never press through the ball complement. A 40° bearing wants a genuine axial load to keep the balls tracking properly, so running one nearly unloaded at speed invites skidding.

Interchange guidance

New Departure Hyatt was General Motors’ bearing division and is long out of production, so cross-reference by the ISO number: 7210B at 40°, supplied as a tandem duplex set. Genuine same-angle equivalents include SKF 7210 BEP and 7210 BECBP, FAG 7210-B-TVP, NSK 7210B and NTN 7210B, mounted as a DT pair. Related sizes fill the identical 50 x 90 x 20 mm envelope at shallower angles — 7210AC is 25°, 7210C is 15°, and NDH’s own 20210 is the 15° version of this number. Those are different parts with far lower thrust capacity, not substitutes. The arrangement code matters just as much: a DB or DF pair of this size handles reversing thrust instead of doubling it in one direction, and will not do this job.