Timken/Fafnir 2MM vs 3MM: Read the Part Number, Pick the Bearing

The difference between a 2MM and a 3MM is one digit and ten degrees. Get it wrong and the spindle tells you fast.

How to read a Timken or Fafnir super precision bearings part numbers, digit by digit, and pick the right replacement.

A spindle comes in for rebuild. The old bearings say 2MM9110WI DUL. The quote sheet says 3MM9110WI DUL, because it was “close enough” and in stock.

It isn’t close enough.

Fafnir super precision bearings pack contact angle, precision class, series, bore, construction and preload into one string. Every character changes how the spindle runs. Here’s how to read it.

2MM vs 3MM: The First Digit Decides the Spindle

Start at the front of the number.

• 2 = 15° contact angle. Built for speed. Lower axial stiffness, higher speed capability. The usual pick for grinding and high-RPM spindles.
• 3 = 25° contact angle. Built for thrust. More axial stiffness and load capacity, less top-end speed. Common in milling and heavier-cut spindles.

That split comes straight from the Timken Fafnir machine tool catalog: most types come in 15° (the 2 prefix) or 25° (the 3 prefix).

“They’re the same size, it’ll fit” is what the parts counter tells you. “You just changed the spindle’s stiffness, heat and speed limit” is what the machine tells you three weeks later.

Match the angle. Every time.

MM, MMV, MMX: the precision class

The letters after the digit set the tolerance class:

• MM / MMV: Timken’s super precision class (ISO P4S). Running accuracy to ABEC 9 (ISO P2), other features held to ABEC 7 (ISO P4).
• MMX: ultra precision, made to ABEC 9 (ISO P2) throughout.
• MV / V: lower classes, ABEC 7 and ABEC 5.

Going up a class is usually fine. Going down a class on a precision spindle is how a rebuild comes back.

9300, 9100, 200, 300: the series

The series number sets the cross-section, from thinnest to heaviest:

• 9300 ultra-light (ISO 19, the 71900 equivalent).
• 9100 extra-light (ISO 10, the 7000 equivalent). The 99100WN variant sits in the same ISO 10 dimension series.
• 200 light (ISO 02, the 7200 equivalent).
• 300 medium (ISO 03, the 7300 equivalent).

The last two digits are the bore code. From 04 up, multiply by five: 2MM207 is a 35 mm bore, 2MM9110 is 50 mm. Below 04 the codes are fixed: 00 is 10 mm, 01 is 12, 02 is 15, 03 is 17.

WI, CR, DUL: Read the Back Half Too

The back half of the number is where most wrong orders start.

• Construction (WI, WN, HX). WI is the standard, capacity-first design. HX is Timken’s high-speed design. WN sits between the two. Don’t swap them without checking the spindle’s speed and load.
• Cage (CR). Many current numbers carry a cage code such as CR. Some older Fafnir bearings often don’t. Same bearing family, different print.
• Set (SU, DU, TU, QU). Single, duplex pair, triplex or quadruplex set. Universal flush-ground sets can be mounted back-to-back (DB), face-to-face (DF) or tandem (DT).
• Preload (X, L, M, H). The last letter. Extra-light through heavy. DUL is a light-preload duplex pair. DUM is medium.

Put it together: 2MM9110WI CR DUL is a 15°, super precision, extra-light series, 50 mm bore, standard WI construction, duplex pair, light preload.

One more trap: the old Fafnir number on the box and the current Timken number in the catalog don’t always print the same way. Spaces move, cage codes get added, letters get dropped. A 2MM9110WIDUL on a dusty box and a 2MM9110WI CR DUL on a quote can be the same family or not. Read it character by character, not at a glance.

Change one letter and you have a different bearing. That’s why the full model number matters more than the size.

Where to Find Fafnir Super Precision Bearings Fast

A lot of the Fafnir numbers maintenance teams still need aren’t sitting on a distributor shelf. Lead times on precision bearings can stretch for weeks. The spindle doesn’t wait.

That’s where surplus comes in. Plants overbuy spindle spares, retire machines, and the bearings stay new in the box. Entire crates of angular sets sit in warehouses for years.

1. Write down the full number.
   • Prefix digit (2 or 3), precision class, series and bore code.
   • Construction, cage, set and preload letters.
   • If the ring is worn, pull the number off the box or the rebuild record.
2. Match exactly, then decide on substitutes.
   • Contact angle and preload: match them.
   • Precision: same class or higher.
   • Cage code: an older print without CR is often the same bearing family. Confirm with your rebuild shop.
3. Buy from stock you can see.
   • Central Surplus stocks 1,000+ Fafnir part numbers, mostly new old stock.
   • Priced 50 to 90% under distributor price, with same-day shipping on in-stock orders.
   • Browse our Fafnir parts or the full range of super precision angular contact bearings.

Who else has a 2MM duplex pair on the shelf today, and ships it today? Find your part.

Quick answers

What is the difference between Fafnir 2MM and 3MM bearings?
2MM bearings have a 15° contact angle for higher speed. 3MM bearings have a 25° contact angle for more axial stiffness and thrust capacity.

What does DUL mean on a Fafnir bearing?
DU is a universal duplex pair. L is light preload. DUM is medium preload, DUH heavy.

Can I replace a 2MM with a 3MM?
Not without changing how the spindle behaves. Match the contact angle to the original.

Are new old stock Fafnir super precision bearings safe to use?
New old stock is new and unused. Check the box, the seals and the grease age, especially on sealed bearings that sat for years.

What other brands interchange with Fafnir?
Most brands like SKF, NSK, NTN, FAG and of course Timken. The 9100 series lines up with ISO 7000-series bearings from other makers. See our bearing cross reference chart before swapping brands.

Fafnir super precision bearings reward the buyer who reads every character.

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