RHPLJT2.1/4Inch Series Single Row Angular Contact Ball Bearing 2-1/4 x 4-1/2 x 7/8 in, Open

Product Description

What this part is

An inch-series single-row angular contact ball bearing, 2-1/4 in bore × 4-1/2 in outside diameter × 7/8 in width, open construction with no seals or shields. Angular contact ball bearings carry radial load together with axial load in one direction only. The rings are non-separable but the raceways are offset, with one high and one low shoulder on each ring, so the bearing cannot locate a shaft by itself — it must be opposed by a second angular contact bearing or by a locating bearing elsewhere on the shaft.

Decoding the designation

LJT – RHP’s inch-series single-row angular contact ball bearing family. The related LJ prefix is the inch-series deep groove family; LJT is the angular contact variant of the same imperial envelope range.
2.1/4 – the bore expressed in inches, 2-1/4 in. RHP’s inch designations use a full stop where other systems use a dash or a space.
M / MB – cage variants. On RHP inch bearings these letters denote a machined brass cage rather than the standard pressed cage. Which of the two, if either, applies to the pieces in stock has not been confirmed against the physical bearing, so no cage material is published as fact.

Correcting the source data

Two corrections have been made.

First, the previous description called this a plain ball bearing and framed it as a general-purpose radial unit. The LJT prefix identifies it as an angular contact bearing, which is a materially different part with different mounting requirements — it is orientation-sensitive and needs an opposing bearing. That has been corrected.

Second, the source data disagreed with itself on width: the title stated 7/8 in while the description stated 1 in. Manufacturer and distributor catalogue data for the LJT2.1/4 give the boundary dimensions as 2-1/4 × 4-1/2 × 7/8 in, so the 7/8 in figure is correct and the 1 in figure has been removed. The incorrect figure is noted here only so that anyone who saw the earlier listing knows which number to trust.

What these specs mean in practice

The inch envelope is the reason this bearing exists in a market otherwise dominated by metric sizes. A 2-1/4 in bore is 57.15 mm and a 4-1/2 in outside diameter is 114.3 mm; there is no metric bearing that lands on those figures, so on legacy British and imperial machinery an inch-series bearing is not a preference, it is a requirement. Trying to shim a nearby metric size into an imperial seat gives up the fit that makes the bearing work.

On the angular contact side, the thing to understand is that this bearing takes thrust in one direction only. Mount it backwards and it will attempt to carry the load over the low shoulder, which fails quickly. Mount it without an opposing bearing and the shaft is not located at all.

Published ratings and mounting data

Figures below come from distributor catalogue data for the LJT2.1/4 rather than a manufacturer publication, so treat them as provisional.

Basic dynamic load rating (C): approximately 65.5 kN
Basic static load rating (C0): approximately 48.2 kN
Limiting speed, grease: approximately 3 200 r/min
Limiting speed, oil: approximately 6 400 r/min
Approximate mass: 1.09 kg

Contact angle and precision class are not published in the sources located and are therefore left blank rather than estimated. The static rating sitting below the dynamic rating is normal and is not a data error.

Quantity and configuration

Two bearings on hand, stocked as individual pieces. They are not represented as a factory-matched or preloaded duplex set; a duplex mounting needs bearings matched by the manufacturer for preload and flush faces, and two unmatched singles will not deliver a specified preload even with identical part numbers.

Fitting notes

Identify the high and low shoulders before assembly and fit the bearing facing the direction the thrust actually comes from. Press only against the ring taking the interference fit; never drive mounting force through the balls. If the cage turns out to be machined brass, it is more tolerant of shock and high temperature than a pressed steel cage but less forgiving of careless handling. Open bearings ship with a preservative rather than a service lubricant, so grease or oil before running.

Interchange guidance

RHP was acquired by NSK, and RHP-designated inch bearings are catalogued and supported through NSK. The LJT2.1/4 designation and its 2-1/4 × 4-1/2 × 7/8 in envelope are the reference point for any substitute — check the boundary dimensions in inches, not a metric approximation. Cage variant and contact angle are the remaining differentiators and should be matched to the original where the application is speed- or thrust-critical.