NTN7903T1GGMP5Super-Precision Angular Contact Ball Bearing – 17 mm ID, 30 mm OD, 7 mm Width, Open, ABEC 5 / P5, Medium preload, Universal grinding

Product Description

What this part is

NTN 7903T1GGMP5 is a single-row super-precision angular contact ball bearing on the metric 79 extra-light series, bore 17 mm, outside diameter 30 mm, width 7 mm. The ISO envelope designation is 71903. The bore is straight, both faces are open, and the rings and balls are high-carbon chrome bearing steel. Running accuracy is ISO class 5, ABEC 5 in the ANSI scheme.

Decoding the designation

The 7903 root fixes the 79-series envelope on a 17 mm bore. In the NTN order code that follows, G marks universal grinding, so the faces are ground to let any two or more bearings of the designation be stacked back-to-back, face-to-face or in tandem without spacers or shims. GM is the medium preload group. P5 is the running-accuracy class. The carton also carries the interchange designation 3MM9303WI CR SUM, in which SU reads as single universally ground and M again as medium preload — the two schemes cross-confirm each other on grinding and preload.

What these specs mean in practice

Universal grinding with a defined preload group is what makes a spindle stack repeatable: the preload is built into the ground faces at the factory, so clamping the rings solid against square shoulders produces the catalogue stiffness without a measured shim stack. Medium preload sits between the light group, which favours speed and runs cooler, and the heavy group, which buys stiffness at the cost of heat and speed. Class 5 accuracy holds bore, outside diameter and raceway runout to a small fraction of standard tolerance, so the seats have to be ground to match for the accuracy to reach the tool.

Load and speed data

Basic dynamic capacity is 4.8 kN, 1,079 lbf. Basic static capacity is 3.1 kN, 697 lbf. Limiting speed is 45,000 rpm with oil, which is the figure the small 79-series section and the light ball complement are designed to reach. Mass is roughly 0.04 lb.

Quantity and configuration

1 Pc. One single bearing, one row, universally ground. It runs alone or as a member of a ground stack built from further bearings of the same designation and preload group.

Fitting notes

Mounting is done clean, with the rings pressed only on the ring being fitted and the outer ring clamped square against a ground shoulder. In a duplex or tandem stack the marked faces are indexed together in the arrangement chosen. Oil-air, oil-mist or a light grease charge suits the open construction; the open faces are what allow the through-flow at high speed.

Cross-references

Every machine tool bearing maker builds super-precision bearings on the 71903 envelope, and the carton designation 3MM9303WI CR SUM is the Timken/Fafnir WI series cross-reference. A 71903 or 7903 with a different preload group, a different accuracy class or a different angle code is a related size in the same envelope, because preload group and angle set stiffness and speed together.