NSKThin Section Super Precision Angular Contact Ball Bearing Matched Pair 55x80x13 mm 15° ABEC 7 Light Preload

Product Description

What this part is

A duplex-ground matched pair of single-row super-precision angular contact ball bearings in the thin-section 719 range. Each bearing is 55 mm bore, 80 mm outside diameter, 13 mm width, ground to a 15° contact angle and a light preload band, with a polyamide cage. The pair clamps as one unit at 26 mm total width.

Decoding the designation

The 719 prefix and bore code 11 give ISO dimension series 19 at a 55 mm bore, which is why the bearing is also designated 71911. In the NSK scheme C denotes a 15° contact angle, TY denotes a ball-guided polyamide cage rated to a 120 °C ceiling, DU denotes duplex universal grinding, L denotes the light preload grade, and P4 denotes super-precision tolerances to ABEC 7 / ISO class 4.

What the 719 series buys

The dimension series is the defining feature here. At a 55 mm bore the 719 section is only 12.5 mm of radial wall and 13 mm wide, against a 70-series 7011 at 90 mm outside diameter and 18 mm wide. That slim section is what lets a spindle designer put a large-diameter shaft through a small housing bore, raising shaft stiffness without growing the assembly. The trade is capacity: smaller balls in a thinner ring carry less load, so a 719-series bearing is chosen for stiffness-per-envelope and speed rather than for load rating.

What these specs mean in practice

A 15° contact angle is the speed-biased choice, keeping ball centrifugal and gyroscopic effects low so the pair reaches a higher limiting speed and runs cooler than a 25° pair of the same envelope, at the cost of axial capacity and axial stiffness. That pairs naturally with the thin section, since both choices point at high-speed service.

A polyamide cage is the quiet, low-friction option. Polyamide is light and self-lubricating against the balls, tolerates momentary lubrication starvation better than steel, and damps cage noise, with ball guidance keeping it centred by the ball set itself. Its limit is the roughly 120 °C ceiling, and long exposure to hot oil degrades it, which makes cage material a genuine selection criterion rather than a detail.

Light preload adds the least friction heat of the preload grades. P4 holds bore, outside diameter, width and running accuracy to single-digit micron limits, and duplex grinding converts those tolerances into the preload: the ring faces are relieved by a measured amount, so clamping the pair solid produces the light preload directly with no shimming.

Quantity and configuration

Matched pair, 2 Pcs, duplex ground as one set.

Fitting notes

The pair is assembled in the orientation its face marks indicate, most often back-to-back for moment stiffness, and the inner rings are clamped solid so the ground relief sets the preload. A thin-section ring is less forgiving of an out-of-round or over-tight seat than a heavy one, since the ring deflects to match the seat and carries that distortion into the raceway, so seats are ground and measured. Mounting heat is worth watching on a polyamide-caged bearing, since heating a ring well past the cage limit damages the cage rather than the steel.

Interchange guidance

71911 is the ISO base designation for this envelope, and 7911C is the same bearing in NSK’s short form. 2MM9911WI is the Fafnir-scheme number for the same 15° 719-series position. Same-envelope bearings differing in contact angle, cage, preload grade or tolerance class — the 25° and 30° variants, the phenolic-caged TR forms, the medium and heavy preload grades, and P5 class pieces — are related sizes rather than interchanges. The 70-series 7011 shares the 55 mm bore in a much heavier section and is a different load class, not a substitution.