NTN7211DBGNP4Angular Contact Ball Bearing Matched Pair – Straight Bore, 55 mm ID, 100 mm OD, 21 mm Width Each, 42 mm Total, Back-to-Back, Normal Preload, P4

Product Description

What this part is

An NTN 7211-DB-GN-P4 matched pair of single-row angular contact ball bearings, ground and supplied together as a back-to-back duplex set. Bore 55 mm, outside diameter 100 mm, 21 mm wide per bearing and 42 mm across the mounted pair, open on all faces, phenolic cages, P4 super-precision.

Decoding the designation

7211 is the ISO base number in the 72 dimension series, bore code 11 giving 55 mm. DB is the back-to-back duplex arrangement. GN is normal preload in the NTN super-precision preload range, which runs light, normal, medium, heavy. P4 is ISO class 4 accuracy, equivalent to ABEC 7.

What these specs mean in practice

A single angular contact bearing takes thrust one way only. Mounting two back-to-back puts the load lines apart in a diverging pattern, which locates the shaft axially in both directions and gives a wide effective bearing spread, so a back-to-back pair resists overhung and moment loading better than a face-to-face pair of the same size. The faces are ground so that clamping the rings solid brings the set to a defined normal preload without shims: that removes internal play, raises axial and radial stiffness, and holds ball-set position at speed. P4 accuracy keeps bore, outside diameter and running runout within super-precision limits.

Cage and temperature

Phenolic cages are light, run quietly with oil and tolerate high speed at low mass, and are the standard choice for ground spindle sets. The record data puts continuous service between –30 °C and 120 °C.

Quantity and configuration

One matched pair, 2 Pcs, ground as a set for back-to-back mounting. Preload is a property of the pair clamped up together.

Fitting notes

The matching marks on the ring faces are lined up and the two bearings are set with their wide outer-ring lands outward for the back-to-back sense. The set is clamped solid at both rings; leaving one ring axially free releases the preload. Handling keeps the two bearings together, since matching is dimensional between those specific rings.

Interchange guidance

The 55 x 100 x 21 mm angular contact envelope is shared by FAG 7211-B-TVP-P4 and SKF 7211 BE/P4. Those are 40° executions and are related sizes rather than substitutions here, since contact angle, cage material and preload grade all have to match for a duplex set to behave as designed. A single 7211 of any brand does not replace half of a matched pair.