NTN7312T1GDB/G03PMPrecision Angular Contact Ball Bearing 60x130x31 mm, 30 Degree Contact Angle, Machined Phenolic Cage, Back-to-Back Duplex Arrangement

Product Description

What this part is

An NTN precision angular contact ball bearing in the heavy 73-dimension series, 60 mm bore × 130 mm outside diameter × 31 mm width, 30° contact angle, fitted with a machined phenolic cage and supplied in a back-to-back duplex arrangement.

Decoding the designation

7312 — 73-dimension series angular contact, 60 × 130 × 31 mm. With no angle suffix, NTN’s standard contact angle for this series is 30°.
T1 — phenolic cage. This is NTN’s own published cage code, and it is the specification worth noticing: NTN’s default is an unmarked pressed-steel cage, J is pressed steel, L1 is machined brass and T2 is moulded resin. T1 puts this bearing in the machine tool and high-speed category.
DB — back-to-back duplex arrangement, with the load lines diverging outward for high moment and tilting resistance.
G03 and PM — undecoded. See below.

Correcting the source data

Two items on the original listing do not survive checking, and it is more useful to say so than to repeat them.

First, the suffix PM is not part of NTN’s published precision numbering. NTN’s precision codes are the unmarked ISO class 0 (ABEC 1), then P6, P5, P4, P2 and PXn. PM appears on the carton and is retained as a search term, but no ABEC or ISO class is claimed from it. Similarly G03 has no published meaning in NTN’s scheme, and GDB is not a single NTN code — NTN publishes G for a universally ground single and DB for a back-to-back arrangement separately, and its universal-pair code is GD2. GDB appears to be a contraction rather than a factory designation. All are kept as search terms and none is decoded.

Second, and more consequentially, the original description offered 2MM312 WI CR DUL as an equivalent. It is not one. In the Fafnir/Timken scheme the 2MM prefix denotes a 15° contact angle, while this NTN 7312 is a 30° bearing. Those are functionally different bearings with different thrust capacity, different stiffness and different speed limits, and swapping one for the other in a spindle would be a real mistake. The designation is retained as a search term only, and is explicitly not an equivalent. Note also that DUL denotes a light-preload duplex pair while this part is designated DB, which is an arrangement rather than a preload class — another reason the two numbers are not describing the same product.

What 30° with a phenolic cage means in practice:
30° is the thrust-biased end of the general-purpose angular contact range: high axial capacity and axial stiffness, good resistance to thrust reversal, at the cost of speed and heat compared with a 15° or 25° bearing. The phenolic cage partly offsets that penalty. Riding light and damping ball-passage excitation, phenolic tolerates marginal lubrication far better than steel or brass and allows higher dN values, which is why it appears on machine tool and high-speed positions. Its constraint is temperature — phenolic is not a high-temperature material, so it is the wrong cage for a hot-running position.

Published ratings and mounting data

Dynamic load rating Cr — 109 kN (single bearing)
Static load rating Cor — 71.5 kN (single bearing)
Fatigue limit load Cu — 5.60 kN
Limiting speed — 5,900 rpm grease, 7,900 rpm oil (single bearing)
Axial load centre offset a — 43 mm
Mass — 1.74 kg
Chamfer rs / r1s minimum — 2.1 mm / 1.1 mm
Abutment dimensions — da 72 mm, db 67 mm, Da 118 mm, Db 123 mm

For a DB, DF or DT pair, NTN publishes set ratings of Cr 176 kN and Cor 143 kN with limiting speeds of 4,700 rpm grease and 6,300 rpm oil. The set’s dynamic rating is about 1.6 times a single’s rather than double, because the two bearings do not share load equally — sizing a pair by doubling the single figure overstates capacity by roughly 20 per cent.

Fitting notes

Mount back-to-back as designated, working to the abutment dimensions above so shoulders clear the ring faces without fouling the cage. Observe thrust direction on each bearing. Because phenolic cages are oil-absorbing and temperature-limited, avoid aggressive solvent flushing and confirm the operating temperature. Bearings ship preserved rather than charged with service lubricant.

Interchange guidance

The same envelope and 30° angle in other schemes: 7312A in NSK format where A denotes 30°, 7312 in FAG format, and 7312BECBM in SKF format — though note the SKF B suffix denotes 40°, so an SKF 7312B is not angle-equivalent to this bearing. Within this envelope, 7312C is 15° and 7312B is 40°, and neither substitutes for a 30° part. NTN remains the current source.