NHBBME-1211DMSuper-Precision Angular Contact Ball Bearing Matched Pair – Straight Bore, 55 mm ID, 100 mm OD, 21 mm Width, Open, 15° Contact Angle, Medium Preload, Phenolic Cage, ABEC 7

Product Description

What this part is

NHBB ME-1211DM is a duplex matched pair of super-precision angular contact ball bearings, 55 mm bore by 100 mm outside diameter by 21 mm width per bearing, 42 mm across the mounted pair. The rings and balls are 52100 chrome steel, the cage is fabric-base phenolic laminate, and both bearings are open with no shield or seal. NHBB is New Hampshire Ball Bearings, a United States super-precision manufacturer.

Decoding the designation

The carton carries three numbering schemes at once, and they agree. NHBB ME-1211DM sits in the metric angular contact series at the MER-211 envelope; the DM suffix is a duplex pair at medium preload. The ISO reading 7211-C-TPA-P4-DUM gives C for a 15° contact angle, TPA for a phenolic laminate cage, P4 for ABEC 7 tolerances and DUM for a duplex universal set at medium preload. The Fafnir reading 2MM211WI-CR-DUM gives 2MM for 15° and CR for a phenolic outer-land-riding cage.

What these specs mean in practice

A 15° contact angle favours speed and radial rigidity over thrust capacity; a 25° bearing in the same envelope would carry more thrust and turn slower. The phenolic cage is light, self-lubricating and tolerant of high speed, and it sets the practical temperature ceiling at 120°C. Medium preload removes internal play and fixes axial position without the heat generation of a heavy preload set.

Quantity and configuration

Two pieces, supplied as one matched pair. Because the set is universally ground, the two bearings can be mounted back-to-back, face-to-face or in tandem, and the ground offsets produce the specified medium preload when the rings are clamped. The set is preloaded rather than clearance-set, so no internal clearance class applies.

Fitting notes

The maximum shaft or housing fillet radius the bearing corners clear is 0.059 in. Inner land diameter is 2.713 in and outer land diameter 3.389 in. Both bearings are non-separable with a relieved outer ring, and either oil or grease lubrication suits the phenolic cage.

Interchange guidance

The Fafnir 2MM211WI-CR-DUM and SKF 7211 CD/P4ADGC are the direct equivalents, matching on envelope, 15° contact angle, ABEC 7 class and medium preload. The SKF 7211 CD/P4ADGB is the same bearing at light preload. A 7211 ACD, 7211 A5 or 3MM211WI is a 25° bearing on the same envelope, so it is a related size rather than a substitution, and a DL or DUL suffix denotes light preload instead of medium.