Fafnir3MM9106WIDUHSuper Precision Angular Contact Ball Bearing Matched Duplex Pair 30x55x13mm 25 Degree ABEC 7 Heavy Preload

Product Description

What this part is

A matched duplex pair of Fafnir 3MM9106WI super-precision angular contact ball bearings, universally ground for heavy preload (DUH). Each bearing is 30 mm bore x 55 mm OD x 13 mm wide, so the pair stacks to 26 mm overall. The 9100WI line is Fafnir’s light-section spindle series on the 7006 envelope, intended for machine tool spindles, grinding heads and precision screw drives.

Decoding the designation

3MM — Fafnir super-precision series, 25° contact angleThe MM prefix implies ABEC 7/9 (P4S) tolerance class, not plain P49106 — 9100 light-section series, 7006 envelope, 30 x 55 x 13 mmWI — super-precision spindle bearing designDUH — duplex, universally ground, heavy preload

What these specs mean in practice

Heavy preload is the stiffness end of the range: it holds the shaft firmly against axial deflection and gives the best positioning accuracy under load, at the cost of more internal friction, more heat and a lower practical speed limit than light or medium preload. The 25° contact angle carries substantially more thrust than a 15° bearing of the same size. Pick DUH only if the spindle design calls for it — fitting a heavy-preload pair where a light one belongs will run hot.

Published specifications

Bore: 30 mmOutside diameter: 55 mmWidth: 13 mm each bearingTotal width mounted as a pair: 26 mmContact angle: 25°Tolerance class: ABEC 7/9 (P4S)Preload: heavy (H)Rows: single row each, mounted as a duplex pairClosure: open

Quantity and configuration

Two bearings, supplied as the factory-matched set. Universally ground rings allow back-to-back (DB), face-to-face (DF) or tandem (DT) mounting while still producing the intended heavy preload. Keep the pair together — the preload lives in the matched grind, not in a spacer, so a split set or a mixed set gives an unknown preload.

Fitting notes

Mark the ring faces before removal so the original orientation can be reproduced. Shaft and housing seats need to be ground to a comparable precision class or the bearing’s accuracy is wasted. Because of the heavy preload, follow the machine builder’s lubrication regime closely and allow a proper run-in; expect a higher steady-state temperature than a light-preload pair.

Interchange guidance

Same-specification alternatives are 7006-envelope 25° ABEC 7 heavy-preload duplex sets, and the 3MM9106WIDUH / 3MM-9106-WI-DUH forms of this number. Related sizes that are NOT drop-in: 2MM9106WI is the same envelope at 15°, and DUL/DUM carry light or medium preload. A 7006A in the NSK scheme is 30° and a different part.