NTNSuper-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 and will come up to a repeatable medium preload.

Decoding the designation

7907 is the ISO angular contact base number in the extra-light 79xx series, 35x55x10 mm.

G and GM are NTN precision, cage and greasing codes. These are NTN-specific and should not be read against another maker’s suffix table.

P4 is the NTN precision class corresponding to ABEC 7.

SUM denotes 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 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.

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.

Mounting data

Preload is ground into the ring faces and is fixed at manufacture; it is not adjustable at assembly.

Quantity and configuration

One bearing is supplied, which matches the S in SUM: this is a single, not a set. SUM states the preload the bearing will produce when it is paired, not how many are in the package.

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 precision class, cage type, contact angle and preload class should be confirmed before substituting. Matching boundary dimensions alone is not sufficient on a precision spindle bearing.