NTN7907GGMP4Super-Precision Angular Contact Ball Bearing 35 x 55 x 10 mm, ABEC 7, Single Universal Grind, Medium Preload, Thin Extra-Light Section

Product Description

What this part is

A single super-precision angular contact ball bearing in the ISO 7907 envelope: 35 mm bore, 55 mm outside diameter, only 10 mm wide. It is ground to P4, which is ABEC 7, and it is universally ground, so two or more can be stacked in any of the standard arrangements straight from the bag and will come up to a repeatable medium preload without shims or measuring.

Decoding the designation

7907 — ISO angular contact base number in the extra-light 79xx series, 35x55x10 mm.
G and GM — NTN precision, cage and greasing codes. These are NTN-specific and should not be read against another maker’s suffix table.
P4 — NTN precision class corresponding to ABEC 7.
SUM — single, universally ground, medium preload. The cross-reference 7907E SUM and the inch-market designation 3MM9307WI CR SUM carry the same meaning.

Why the 79xx section matters

At 35 mm bore, a 79xx bearing is only 10 mm wide with a 55 mm outside diameter. A 72xx bearing on the same shaft would be substantially thicker and heavier. The extra-light section exists for designs where the radial envelope around the spindle is fixed and there is no room to grow, or where minimising rotating mass matters more than load capacity. The price of that thin section is exactly what you would expect: less load capacity and less stiffness than a heavier series on the same bore, so it belongs in light to moderately loaded, speed-driven positions.

What these specs mean in practice

Medium preload sits between light and heavy. Compared with light preload it gives more axial and radial stiffness and better running accuracy under varying load, which matters if the spindle has to hold position under a cutting force. The cost is friction and heat, so medium preload is the wrong choice if the duty is very high speed with minimal load. Because preload is ground into the ring faces, it cannot be adjusted at assembly, and every bearing in a stack must be the same preload class or the load will not share evenly.

The universal grind is the practical benefit. Non-universal precision bearings need measured shims or grinding to set preload in a stack. Universally ground rings are finished so that any two of the same designation, in any orientation, produce the specified preload when clamped face to face. That turns a fitting job that needs a metrology bench into one that needs a torque wrench.

Published ratings and mounting data

NTN does not publish dynamic (Cr) or static (C0r) load ratings, a contact angle or a limiting speed against the 7907GGMP4 designation in any source reachable today. This is a legacy precision designation and its data sat in out-of-print catalogues. We have left those fields blank rather than borrow figures from a current-production 7907 or from another brand, because contact angle and preload class change both ratings and the speed limit materially. Note in particular that the contact angle is not stated in this designation, so do not assume 15° or 30° without checking with NTN.

Quantity and configuration

One bearing is supplied, which matches the S in SUM: this is a single, not a set. The photographs show a single bearing in its original sealed bag, marked Japan. SUM tells you the preload it will produce when it is paired, not how many are in the package.

Fitting notes

A 10 mm wide ring at 55 mm outside diameter is not a stiff object on its own, and it is easy to distort. Support the ring being pressed and press evenly on that ring only, never through the balls. Keep it bagged until assembly; at ABEC 7 the tolerances are a few microns. Shaft and housing seats should be finished to at least the same tolerance class as the bearing, and clamping faces must be square, because a thin-section bearing will faithfully transmit any out-of-square clamping into the running accuracy.

Interchange guidance

Common cross-references for this size and configuration are 7907E SUM and the inch-market precision designation 3MM9307WI CR SUM. Any 35x55x10 mm super-precision 7907 is worth evaluating, but confirm precision class, cage type, contact angle and preload class before substituting. Matching boundary dimensions alone is not sufficient on a precision spindle bearing.