NDHQH0L28EDTL5APrecision Angular Contact Ball Bearings 140x210x30 mm, 25° Contact Angle, DT Tandem Duplex, Light Preload, P5 Class — 7028 Envelope

Product Description

What this part is

New Departure Hyatt precision angular contact ball bearings in the 7028 envelope — 140 mm bore, 210 mm outside diameter, 30 mm width per bearing. Ground for DT tandem mounting at light preload, ISO precision class 5.

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

QH0L28 — NDH’s internal number for the 7028 envelope. The recorded dimensions, 140 x 210 x 30 mm, confirm the 7028 mapping.
E — a 25° contact angle, consistent with the 7028E cross-reference recorded against this item.
DT — tandem duplex: two bearings facing the same way, sharing thrust in one direction.
L5A — NDH preload and variant code. The L indicates light preload and the 5 aligns with the P5 class in the recorded cross-reference; the trailing A has no published decode we could confirm, so it is kept as a search term.

Why the tandem arrangement matters

DT behaves quite differently from the other duplex arrangements. Back-to-back (DB) and face-to-face (DF) sets take thrust in both directions and locate the shaft axially. A tandem set does not. Both bearings face the same way and split one heavy thrust load between them, roughly doubling axial capacity in that direction — while the assembly has to be located axially by something else.

If you fit a DT set where a DB set was intended, the shaft will have no axial location in one direction. Confirm the original arrangement before substituting. Tandem sets typically appear in heavy vertical spindles, screw-down drives and similar one-way thrust positions.

What these specs mean in practice

A 25° contact angle carries considerably more thrust per unit of radial load than a 15° bearing and holds axial position better under interrupted loading, at the cost of a lower speed ceiling and more heat at a given speed. Combined with a tandem arrangement, this set is clearly built for a thrust-dominated position rather than a high-speed one.

P5 controls running accuracy to closer limits than standard class, which matters where the bearing sets a shaft position or where vibration is a concern, though it is a step coarser than the P4/ABEC 7 spindle grades.

Quantity and configuration

The listing title states 2 pieces, consistent with a DT tandem set, while our stock record shows a quantity of 1 — most likely one set of two bearings. Duplex sets in surplus are frequently split, so we are publishing no firm quantity claim and have not altered the inventory record. Contact us before ordering and we will confirm that 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 not substituted figures from a commercial 7028 or from another maker’s 7028E — different internal geometry and class. An honest gap beats a borrowed number.

Fitting notes

Observe the ring markings for orientation. In a tandem set both bearings face the same way; reversing one turns 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 — the preload is built into them. Press only on the ring being fitted, never through the balls, and clamp both rings fully.

Interchange guidance

ISO base number 7028. The recorded cross-reference 7028 E T DUL P5 is a useful search term, though note it specifies DU (duplex universally ground) rather than DT (tandem mounting) — those describe grinding and mounting respectively. When sourcing a replacement, match the contact angle, the precision class and above all the arrangement.