Koyo7905C5GLP4FGSuper-Precision Angular Contact Ball Bearing – 25 mm ID, 42 mm OD, 9 mm Width, 15 degree contact angle, Open, ABEC 7 / P4

Product Description

What this part is

Koyo 7905C5GLP4FG is a single-row super-precision angular contact ball bearing in the metric 79 light series, bore 25 mm, outside diameter 42 mm, width 9 mm. The ISO base designation for this envelope is 71905. Rings and balls are through-hardened chrome steel, the bore is straight, and both faces are open for oil or grease feed.

Decoding the designation

The 7905 root gives the 79-series dimension envelope on a 25 mm bore. The letter C is the Koyo contact-angle code for 15°. P4 is the running-accuracy class, equivalent to ABEC 7 in the ANSI scheme. The 5GL and FG groups are Koyo carton designations carried on this part; they are recorded under carton markings so the exact box number remains searchable.

What these specs mean in practice

A 15° contact angle sets the load line close to the radial plane. That geometry favours speed and radial stiffness and carries less thrust than a 25° or 40° angle of the same size, which is why 15° bearings dominate machine tool and grinding spindles. The P4 class tightens bore, outside diameter and raceway runout well beyond a standard bearing, so shaft and housing seats have to be ground to matching tolerances for the accuracy to appear at the tool.

Quantity and configuration

Single bearing, one row, universally ground faces. It runs alone as a bearing located in one axial direction, or in a ground stack with further bearings of the same designation for back-to-back, face-to-face or tandem duty.

Fitting notes

Precision angular contact bearings are mounted with the high point of eccentricity indexed and the outer ring clamped square against a ground shoulder. Oil-air or oil-mist feed suits the open construction at high speed; light grease charge suits moderate speed. Handling is done clean, in the original wrap, with the axial faces protected.

Interchange guidance

Same-envelope 15° P4 super-precision equivalents include the ISO 71905 C designation used across makers and the Timken/Fafnir 2MM9305WI. A 71905 or 7905 carrying a 25° angle code, a different cage, or a different preload group is a related size in the same envelope rather than a direct substitution, because angle and preload set the stiffness and speed limit.