NDHQ20224DTL7Super Precision Angular Contact Ball Bearings 120x215x40 mm, DT Tandem Duplex, Light Preload — 7224 Envelope

Product Description

What this part is

New Departure Hyatt super-precision angular contact ball bearings in the 7224 envelope — 120 mm bore, 215 mm outside diameter, 40 mm width per bearing. Ground for DT tandem mounting at light preload.

NDH was an American precision bearing maker, long out of production, so these are new old stock against a designation no longer catalogued.

Decoding the designation

Q20224 — NDH’s internal number for the 7224 envelope. The recorded dimensions, 120 x 215 x 40 mm, confirm the 7224 mapping.
DT — tandem duplex. Two bearings mounted face-to-back, both taking thrust in the same direction. This is the key configuration detail.
L7A — NDH preload and variant code. The L indicates light preload; the 7A element has no published decode we could confirm, so it is retained as a search term.

Why the tandem arrangement matters

DT is the least common of the three duplex arrangements and it behaves quite differently from the others. Back-to-back (DB) and face-to-face (DF) sets take thrust in both directions and locate the shaft. A tandem set does not. Both bearings face the same way, sharing a single heavy thrust load between them — roughly doubling axial capacity in that one direction — and the assembly must be located axially by something else entirely.

The practical consequence: if you fit a DT set where a DB set was intended, the shaft will have no axial location in one direction and the machine will not hold position. Confirm the original arrangement before substituting. Tandem sets are typically found in heavy vertical spindles, screw-down drives and similar one-way thrust positions.

Correcting the source data

The original listing described this as a “double-row angular contact ball bearing”. It is not a double-row bearing — it is two single-row bearings ground to be mounted together in tandem. The distinction is real: a true double-row bearing is one unit with one outer ring, whereas these are separate bearings that must be installed in the correct orientation relative to one another.

The listing also carried the cross-reference 7224C T DUL P4. Note that DU (duplex universally ground) and the DT in the primary part number describe different things — DU says the rings are universally ground, DT says the mounting is tandem — but the L preload code is consistent across both. We have published the DT tandem arrangement from the primary part number and retained the other forms as search terms.

Quantity and configuration

The listing title states 2 pieces, which is consistent with a DT tandem set, while our stock record shows a quantity of 1 — most likely meaning one set of two bearings. Because duplex sets in surplus are frequently split, we are publishing no firm quantity claim and have not altered the inventory record. Contact us before ordering and we will confirm whether two matched bearings are physically present.

Published ratings and mounting data

Load ratings and limiting speeds are deliberately blank. NDH is out of production and no manufacturer data is retrievable for this designation. We have specifically not substituted figures from the Timken 2MM224WI cross-reference or from a commercial 7224 — different maker, different internal geometry, different class. An honest gap is better than a borrowed number here.

Fitting notes

Observe the ring markings for orientation. In a tandem set both bearings face the same way; getting one reversed converts the set into a face-to-face pair with entirely different behaviour and destroys the preload scheme. Never shim, lap or regrind the ground faces. Press only on the ring being fitted, never through the balls, and clamp both rings fully.

Interchange guidance

ISO base number 7224. The Timken/Fafnir equivalent recorded against this item is 2MM224WI-CR-DUL, where 2MM indicates 15°, CR a phenolic outer-land-riding cage and DUL a duplex light-preload set — useful as a search term, though note it specifies DU rather than DT. We also hold a Koyo bearing in this identical 120 x 215 x 40 mm envelope at a 40° contact angle; it is dimensionally interchangeable and functionally not, so match on suffix rather than size.