TimkenNA48390-3Tapered Roller Bearing Cone Only, 5-3/8 in Bore, 1.6875 in Cone Width, Class 3 Precision, Stamped Steel Cage – Cup 48320 Not Included

Product Description

What this part is

An inch-series tapered roller bearing cone from the 48300 family: the inner ring with its tapered roller complement and stamped steel cage, in high-alloy bearing steel. It is a single row, open component intended to carry combined radial and one-directional thrust load once it is paired with its cup.

What is included and what is not

This listing is the CONE ONLY. A tapered roller bearing is separable by design: the cone is the inner ring, rollers and cage, and the cup is a separate hardened outer ring that presses into the housing. The cup is NOT supplied here. On its own the cone will not run — there is no outer raceway for the rollers to bear against.

The mating cup for NA48390 is 48320. If your housing already holds a sound, unpitted 48320 cup and you are only replacing the rotating half, this cone is exactly what you want. If the cup is worn, spalled or you are building the assembly from nothing, you need to buy the 48320 as well.

Decoding the designation

NA – Timken cone prefix within the inch tapered series.
48390 – the cone part number in the 48300 series, 5.3750 in bore.
-3 or *3 – Timken precision class 3, a tighter-than-standard tolerance class. This matches the condition note on the carton.

What these specs mean in practice

Precision class 3 tightens bore, outside diameter, width and running accuracy relative to Timken’s standard class. What a buyer gains is lower runout and a more repeatable mounted fit: less shaft wander, less vibration, more consistent load distribution across the rollers and a better chance of hitting a target preload without hand-fitting. It only pays if the shaft and housing are machined to a comparable accuracy — a class 3 cone in a sloppy bore delivers standard-class performance at a premium price.

The maximum shaft fillet radius of 0.14 in is a real fitting constraint, not a footnote. If the shaft shoulder fillet is larger than that, the cone back face will ride on the fillet instead of seating flat on the shoulder, and the bearing will run cocked. Check it before pressing.

Published ratings and mounting data

Bore d: 5.3750 in
Cone width B: 1.6875 in
Maximum shaft fillet radius: 0.14 in
Rows: 1
Cage: stamped steel
Material: high-alloy bearing steel
Closure: open
Precision: Timken class 3
Mating cup: 48320

Published load ratings of approximately 63,600 lb dynamic and 122,000 lb static are ratings for the complete 48390/48320 mounted assembly, not for this cone in isolation. There is no such thing as a load rating for a cone alone, because the rating describes the cone, cup and roller set working together. Do not use these figures to justify a cone-only purchase where the existing cup is of unknown condition or different precision class. No cone-alone rating is published and none is invented here.

Quantity and configuration

The record shows two on hand. Because on-hand counts in this catalogue sometimes track lots rather than individual pieces, treat the exact piece count as requiring confirmation before committing to a multi-unit order.

Fitting notes

Press on the cone bore face only; never drive load through the rollers or the cage. A tapered roller bearing has no internal clearance until it is mounted, so radial and axial play is set on assembly by the opposed bearing and shim stack. Cone and cup should ideally come from the same precision class; mixing a class 3 cone with a standard-class cup gives you standard-class geometry. Verify the seating shoulder is square and the fillet radius is within limit.

Interchange guidance

48390 is a widely referenced inch-series cone number and appears from multiple manufacturers on the same boundary dimensions. Cross-brand substitution of a cone into an existing cup is generally not recommended unless the two are confirmed as an interchangeable pair; taper angle and raceway finish must match. Numbers to search alongside this one: 48390, NA48390, NA48390-2, NA48390-3, and the cup 48320. Fafnir bearing numbers now sit under Timken following acquisition.