NTN7311T1GDB/G025PMAngular Contact Ball Bearing – 55 mm ID, 120 mm OD, 29 mm Width, Open, Straight Bore, Ground for Back-to-Back Duplex Mounting

Product Description

What this part is

NTN 7311T1GDB/G025PM is a single-row angular contact ball bearing on the metric 73 medium series, bore 55 mm, outside diameter 120 mm, width 29 mm. The bore is straight, both faces are open, and the rings and balls are high-carbon chrome bearing steel. The faces are ground for back-to-back duplex service, so a pair of them clamped together forms one rigid bearing unit 58 mm wide overall.

Decoding the designation

The 7311 root fixes the 73-series envelope on a 55 mm bore. DB is the NTN code for a back-to-back duplex arrangement: the wide faces of the two outer rings meet, the load lines diverge outward, and the pair takes thrust in both directions and carries moment load. The trailing -1/2PR states the sale unit — one bearing of the matched pair. The T1, G025 and PM groups are NTN carton designations recorded as carton markings so the exact box number stays searchable.

What these specs mean in practice

Back-to-back is the arrangement chosen when a shaft has to resist tilting: the diverging load lines put the effective bearing centres outside the physical bearing, which gives the pair a wide support base and high moment stiffness in a short axial length. Face-to-face converges the load lines instead and tolerates a little more misalignment with less moment stiffness, and tandem stacks the load lines parallel for thrust in one direction only. Because the pair is factory ground to a set preload, the two rings are clamped solid against square shoulders rather than adjusted at assembly.

Quantity and configuration

1 Pc. One bearing out of a back-to-back matched pair, single row, ground faces. A complete DB unit uses two bearings of the same designation and preload group.

Fitting notes

The pair is assembled with the marked faces indexed as etched, the inner rings clamped by a locknut and the outer rings clamped by an end cap, both against ground shoulders. Force is applied only to the ring being fitted. Grease or oil is fed through the open faces; the preload set by the ground faces means running clearance is fixed once the rings are clamped solid.

Interchange guidance

The 55 x 120 x 29 mm envelope is shared across makers on the 7311 root, so ISO 7311 designations from other precision makers cover the same seats. NTN 7311B is a related designation on the same envelope with a 40° contact angle, and NTN 7311BDB is the pre-matched 40° back-to-back set; both differ in load line and stiffness from this designation, so they are related sizes rather than direct substitutions. A 7311 in a different preload group or accuracy class is likewise a related size.