Fafnir3MM226WI-3-MBR-DUMSuper Precision Angular Contact Ball Bearing 130 x 230 x 40 mm, 25° Contact Angle, ABEC 7/9, Machined Bronze Cage, Duplex Medium Preload, Matched Pair

Product Description

What this part is

A matched pair of super precision angular contact ball bearings in the 7226 envelope — 130 mm bore, 230 mm outside diameter, 40 mm width per bearing. These are spindle-grade bearings, universally ground so the two rings can be mounted in any duplex arrangement and will come up to the intended preload when clamped.

Decoding the designation

3MM — Fafnir super precision series with a 25° contact angle. The MM prefix carries P4S tolerance (ABEC 7 running accuracy with ABEC 9 bore and outside diameter control).
226 — 7226 boundary dimensions, 130 x 230 x 40 mm.
WI — Fafnir super precision angular contact spindle bearing.
MBR — machined bronze cage, outer ring land riding.
DUM — duplex, universally ground, medium preload.

What these specs mean in practice

A 25° contact angle sits in the middle of the spindle range: it carries substantially more thrust than a 15° bearing and gives a stiffer axial response, at the cost of some limiting speed. Medium preload follows the same logic — more stiffness and better rigidity under cutting load than light preload, more heat generated at speed. Pick medium where the spindle is doing heavier work at moderate rpm rather than chasing maximum surface speed.

The machined bronze outer land riding cage is the heavy duty choice in this family. Bronze tolerates marginal lubrication and higher temperature better than a phenolic cage and holds its geometry under high centrifugal load, which is why it turns up on larger bore spindles and on grinding and boring applications. Outer land riding means the cage is guided by the outer ring, so it stays concentric at speed and pumps oil predictably.

Quantity and configuration

This listing is a set of 2 pieces — a duplex pair ground together at the factory. Universal grinding means you can stack them back to back (DB) for maximum moment stiffness, face to face (DF) for tolerance of misalignment, or in tandem (DT) to double the thrust capacity in one direction. Clamping the pair against a shoulder and a locknut develops the built-in medium preload; do not add shims or a spacer unless you intend to change the preload deliberately.

Fitting notes

Super precision bearings live or die on the mounting. The shaft and housing seats need to be ground to matching precision with runout held to a few microns, or the bearing’s own accuracy is thrown away. Mount clean, mount with heat or a press on the correct ring, never drive load through the balls, and keep the pair oriented as marked — the ground faces are matched and reversing one bearing changes the preload. Lubricate with a spindle grease or oil mist rated for the intended speed; over-greasing a preloaded pair is a common cause of early heat failure.

Interchange guidance

Fafnir is now part of Timken, and Fafnir super precision numbers are still used and still cross referenced. Same-envelope 25° equivalents from other makers include NSK 7226A5, FAG B7226-E-T-P4S, SKF 7226 ACD/P4A and NTN 7226 in the corresponding precision grade. Those are dimensional and contact angle equivalents; cage material, preload and lubrication codes vary between brands, so match the full order code if you are replacing one half of an existing pair. The -3 element in the source designation is a customer or order specific suffix and is carried here as a searchable reference rather than published as a specification.