NDHMatched Tandem Set, Angular Contact Ball Bearings 55 x 90 x 18 mm, ABEC 5, 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 7011 envelope — 55 mm bore, 90 mm outside diameter, 18 mm width per bearing. Open, ABEC 5 precision, quiet-running selection. Both bearings are ground together as one set to sit side by side facing the same way, which roughly doubles the thrust capacity of a single-direction position. New old stock American spindle-grade product.

Decoding the designation

0L11 — NDH’s designation for the ISO 7011 size, 55 x 90 x 18 mm.
Q — NDH quiet-running selected series, screened for low noise and vibration.
H — NDH ring and grinding variant prefix.
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.
L5 — NDH tolerance grade, equivalent to ABEC 5.

What these specs mean in practice

Tandem mounting is what you use when one-direction thrust exceeds what a single bearing will carry. Both bearings face the same way and share the axial load roughly equally, so capacity climbs sharply — but in that one direction only, so the shaft still needs something opposing at the other end. That is the opposite trade from a back-to-back pair, which handles reversing thrust and resists moment loads without adding capacity in either direction. It also means the two bearings are not interchangeable with two loose singles: they were ground as a set so that the load actually splits evenly instead of the first bearing taking most of it. ABEC 5 running accuracy is a clear step above standard, tight enough for a working spindle, and it only reaches the shaft if the seats are ground and true to match — a worn housing bore erases the benefit. The Q quiet-running selection keeps noise and transmitted vibration low on top of that, which is why this grade appears on motor, instrument and measuring-head positions.

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 converts 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, because 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 55 mm bore onto a tight shaft, and never press through the ball complement.

Interchange guidance

New Departure Hyatt was General Motors’ bearing division and the brand is long out of production, so buyers cross-referencing to a current maker work from the ISO envelope: 7011, 55 x 90 x 18 mm, mounted as a tandem duplex set. The numbers carried on this listing for that envelope are NSK 7011A and 7011A5, SKF 7011 ACD and Fafnir/Timken 3M9111WI CR, all in the 25–30° part of the range. Note that contact angle is the specification to confirm against your own drawing before ordering, because the same 55 x 90 x 18 mm envelope is also built at 15° as 7011C, 7011 CD and 2MM9111WI. Those shallower builds are related sizes rather than substitutes — same fit, materially less thrust capacity and higher speed capability. The arrangement code matters equally: a DB or DF pair of this size handles reversing thrust instead of doubling it in one direction.