Many small machines carry a shaft on two miniature bearings mounted side by side. It is a cheap and simple arrangement. When the machine runs faster, some customers replace the pair with one custom double row bearing that has two raceways in one set of rings. This article explains what changes and when it is worth doing. Catalog sizes are on our small double row bearings and MR miniature bearings pages.
Two bearings, or two rows in one bearing
Two separate bearings each have their own clearance, their own size tolerance and their own fit. In a double row bearing both raceways are ground in the same rings, so their spacing and alignment are set at the factory.
Why a side-by-side pair can give trouble at speed
- The two bearings rarely share the load equally. Small differences in clearance, bore and outside diameter decide which bearing carries more.
- The axial position of each bearing depends on the shaft shoulder, the housing and any spacer. These tolerances add up.
- At higher speed, an unequal load share shows up as heat and noise in one of the two bearings.
What one double row bearing changes
- One outer ring and one inner ring hold both rows. The distance between the rows does not depend on the assembly.
- The internal clearance is set once, for the whole bearing.
- Assembly has one part to press in instead of two, and the two rows cannot be mounted in the wrong order.
- The width can match the space the pair used before, so the shaft and housing often need no change.
Two custom jobs we have made
Double row 608 for textile machines
We made a double row bearing in the 608 size range for textile machinery customers.
Each of these started from the space the customer already had: the shaft diameter, the housing bore and the width available for the bearings.
When it is worth changing
- The pair runs hot or noisy after the speed was raised.
- One bearing of the pair fails first, again and again.
- The assembly needs a spacer or shims to set the pair, and the result varies from machine to machine.
- The volume is large enough that a custom size pays back.
What to send for a quotation
- The two bearings used now, and how they are mounted (photo or drawing).
- Shaft diameter, housing bore and the width available.
- Speed, load direction and running temperature.
- Seal or shield, grease and precision required.
- Annual quantity.
Frequently Asked Questions
Is a double row bearing always better than two single bearings?
No. Two bearings set further apart resist tilting better. A double row bearing is the better choice when the two bearings already sit side by side and space is short.
Can you keep our shaft and housing unchanged?
In most cases we design the double row bearing to the same bore, outside diameter and total width as the pair it replaces.
What is the minimum quantity for a custom miniature double row bearing?
It depends on the size and whether we have suitable rings and balls. Send the details and we confirm feasibility, quantity and lead time.
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Published 2026-11-09. Images show representative products. Final dimensions, grades and supply conditions are confirmed against the drawing and order.