Timken39250/39412BImperial Tapered Roller Bearing Cone & Cup Set, 2-1/2″ Bore x 4-1/8″ OD x 0.8438″ Wide, 115 kN Dynamic

Product Description

What this part is

A Timken single-row imperial tapered roller bearing supplied as a cone-and-cup set: cone 39250, cup 39412. The cone carries the rollers and cage on the inner ring; the cup is the loose outer race. Both go in separately, which is what makes tapered roller bearings the default choice for gearboxes, wheel ends and any shaft support that has to be built up in stages.

Decoding the designation

39250 — the cone (inner ring, rollers and cage).39412 — the mating cup (outer ring).B suffix on 39412-B — a cup design revision. Both 39412 and 39412-B appear in the market at these boundary dimensions and are catalogued against the same 39250 cone, so a machine built for one takes the other at the housing bore. The suffix is retained in the title and cross-references because it is printed on cartons and buyers search it.39250-20024 — a distributor stock number for the cone that turns up in searches; retained as a cross-reference.

Published ratings and mounting data

Bore (d): 2.500 in / 63.50 mmCup outside diameter (D): 4.125 in / 104.78 mmAssembled width (T): 0.8438 in / 21.43 mmCone width through bore (B): 0.8661 inCup width (C): 0.625 inDynamic radial load rating C1: 115,000 N (approx. 25,800 lbf)Static radial load rating C0: 120,000 N (approx. 27,000 lbf)Material: through-hardened bearing steel

What these specs mean in practice

Read the width against the diameter and the character of this bearing becomes obvious. A 2-1/2 in bore bearing only 0.8438 in wide, carrying 115 kN dynamic, is a high-capacity-for-envelope design — the rollers are doing a lot of work in a narrow band. That is the whole point of the tapered geometry: the roller contacts the raceway along a line rather than at a point, so load capacity per unit width is far higher than a ball bearing of the same bore. Substituting a deep-groove ball bearing into a housing designed around this part will not carry the load, whatever the bore says.

The near-parity between dynamic and static ratings, 115 kN against 120 kN, is worth noting when the application involves shock or standing load rather than continuous rotation. Static rating governs when the bearing is stationary or oscillating slowly and the failure mode is brinelling of the raceway rather than fatigue. A press, a slewing joint or a rarely-indexed shaft is sized on C0.

Thrust capacity acts in one direction only. Two of these bearings opposed — back-to-back or face-to-face — hold the shaft both ways and let you set a specified endplay or preload. A single unit facing a reversing axial load will lift its rollers off the raceway on the reverse stroke and skid.

Quantity and configuration

Two sets in stock, which is the natural buy for this part: most shafts use an opposed pair, and replacing both at once means the setting is established with two components of equal wear rather than one new bearing carrying the geometry of an old partner. Sold individually if you only need one.

Fitting notes

Endplay or preload is determined at assembly by the shoulder-to-shoulder distance in the housing, so the 0.8438 in assembled width is a reference figure rather than a setting. Press only on ring faces, never through the rollers. Cones normally take an interference fit on the shaft and cups a light interference or tight slip fit in the housing; use the published fitting practice for your load class instead of a rule of thumb, because an over-tight cup on a tapered bearing pinches the roller path and destroys the setting you just made.

Interchange guidance

Search forms include 39250/39412, 39250-39412, 39250 39412, 39250/39412-B, 39412B, and the loose components 39250 and 39412. NTN catalogues the same set at the same envelope under the identical 39250/39412 numbers, as do Koyo and other inch-series makers, because the 39000 series is an industry standard rather than a proprietary Timken design. Timken acquired the Fafnir and Torrington bearing lines, so a machine originally specified with either brand will list inch-series tapered bearings under numbers Timken still supplies.