When most people in the bearing industry think of a standard deep groove ball bearing, numbers like 6205, 6308, or 6004 probably come to mind. Those familiar metric designations have become a common language across manufacturers and industries around the world.
But bearings have been around longer than today's metric standards.
Open an older electric motor, pump, gearbox, agricultural machine, conveyor, or piece of industrial equipment and you may discover something very different stamped on the bearing:
R8. RLS10. RMS8. LS10. MS10. XLS. NICE 1620.
Welcome to the world of inch-dimension ball bearings.
These bearings are not simply metric bearings whose dimensions have been converted to inches. They belong to dimensional series developed for machinery built around fractional-inch shafts and housings.
Some of the designations date back through generations of bearing manufacturers. Some follow different numbering conventions despite representing dimensionally equivalent bearings. And, just to make things interesting, the same letters can mean different things depending on the manufacturer.
In other words, inch-series bearings can become a little bit of industrial archaeology.
And many are still very much in service.
Inch-dimension ball bearings are bearings manufactured around fractional-inch bore, outside diameter, and width dimensions rather than metric dimensions. They were widely used in older American and British machinery and remain important as replacement bearings for legacy equipment. Common inch-series designations include R, RLS, RMS, LS, MS, LJ, MJ, XLS, and NICE 1600 Series. Because designation systems vary by manufacturer, the bearing's dimensions, construction, manufacturer, and application should be verified before selecting a replacement.
Bearing standardization did not happen overnight.
During the growth of industrial manufacturing in the late 19th and early 20th centuries, American and British machinery was commonly designed around inch dimensions. Shafts, housings, fasteners, tooling, and bearings followed accordingly.
Metric bearing dimensions eventually became dominant internationally, and standardized metric series became increasingly familiar throughout industry.
But there was one small problem.
The machines didn't disappear.
A machine designed around a 1-inch shaft still required a bearing with a 1-inch bore. A housing machined for a particular imperial outside diameter did not suddenly accept the nearest metric bearing simply because newer equipment had moved toward metric dimensions.
The need for replacement inch bearings lasted long enough that British Standard BS 292-2:1982 specifically maintained dimensions, tolerances, clearances, and reference symbols for inch-series ball and cylindrical roller bearings to facilitate procurement of replacement bearings. The standard carried forward inch-series information from the earlier BS 292:1969 and was eventually withdrawn in 1997.
That history helps explain something we still encounter today:
Older standards can disappear from new machine designs without disappearing from maintenance departments.
The R Series is one of the more recognizable families of inch-dimension radial ball bearings. These are deep groove radial ball bearings built around fractional-inch dimensions.
A few examples show the progression:
Published inch-series bearing tables confirm these dimensions. They also reveal an important detail: depending on the bearing and manufacturer, the width of an open R-Series bearing may differ from its shielded or sealed counterpart.
That is our first reminder that recognizing the basic series is only the beginning of bearing identification.
An R8 isn't an 8 mm bore bearing.
It has a 1/2-inch bore.
That distinction may be second nature to an experienced bearing salesperson, but it can be an easy trap for someone who has only worked with modern metric nomenclature.
Move into other imperial deep groove families and two additional designations appear frequently:
RLS and RMS
These represent established light- and medium-section imperial deep groove ball-bearing families.
The difference becomes obvious when we compare bearings designed for the same shaft.
For a 1-inch bore:
RLS8:
1" bore × 2-1/4" OD × 5/8" width
RMS8:
1" bore × 2-1/2" OD × 3/4" width
Both fit a 1-inch shaft, but they do not occupy the same dimensional envelope. Current imperial bearing catalogs continue to list these dimensions and offer RLS and RMS products in open, shielded, and sealed configurations.
That gives us one of the most important lessons in identifying older inch bearings:
Knowing the bore is only the beginning.
If someone walks into a bearing shop and says, "I need a bearing for a one-inch shaft," that is useful information.
It is not enough information.
We still need the OD, width, construction, closure, and preferably the complete markings from the original bearing.
This is where inch-bearing identification gets more interesting.
LS and MS are additional designations associated with light- and medium-section inch bearings.
Published interchange information demonstrates how different manufacturers could identify the same dimensional bearing using very different numbers.
Consider a few examples:
These dimensional relationships are documented in modern inch-series interchange tables.
Look carefully at the one-inch light-series example:
LS10 = RLS8 = LJ1
Three numbers.
One nominal bore.
Three completely different numbering conventions.
And that is exactly why old bearing numbers sometimes create confusion.
The LJ and MJ designations belong to another important chapter in British bearing history.
Ransome & Marles became one of Britain's major bearing manufacturers. In 1969, Ransome & Marles, Hoffmann Manufacturing, and Pollard Ball & Roller Bearing Company were combined into Ransome Hoffmann Pollard, or RHP. NSK later purchased the RHP group in 1990.
Within this tradition, LJ identifies the light-series family and MJ the medium-series family.
Their numbering system is particularly intuitive because the designation can state the bore directly:
Current bearing listings still show dimensional equivalency between LJ and RLS numbers. For example, both LJ1 and RLS8 refer to a 1-inch × 2-1/4-inch × 5/8-inch bearing.
Now compare that with LS10.
Same dimensional family.
Very different number.
There has never been one simple rule for decoding every inch-series bearing designation.
Some numbering systems encode the bore relatively directly.
Others use a series size code.
That is why the part number is valuable, but it should not be the only evidence used to identify an old bearing.
And then there is XLS.
This designation deserves special attention because XLS has not meant exactly the same thing across every bearing manufacturer.
That makes it a perfect example of why the manufacturer's name matters just as much as the letters stamped into the bearing.
Within the Fafnir product lineage, now supported by Timken, XLS identifies an extra-large inch-dimension radial ball-bearing series.
Timken describes these bearings as Conrad-type deep groove designs capable of carrying radial load as well as axial load from either direction.
Current examples include:
That is a significantly different dimensional world from the little R4 we discussed earlier.
But an XLS marking from MRC tells a different story.
The MRC Engineering Handbook identifies XLS as a single-row, 15-degree angular-contact inch-size bearing with a counterbored outer ring.
That means an XLS marking alone does not establish the bearing's internal design.
An MRC XLS and a Fafnir XLS should not be assumed to be the same type of bearing simply because the same three letters appear in the designation.
That's a pretty good bearing-history lesson in three letters.
When dealing with legacy designations, manufacturer matters.
Before replacing an XLS bearing, verify the manufacturer, complete dimensions, internal design, contact configuration, load direction, lubrication requirements, and application.
No discussion of inch-dimension ball bearings would be complete without NICE.
And this is where the history gets especially interesting.
William Nice founded one of America's early anti-friction bearing manufacturing operations in 1902. The company began with unground ball bearings before expanding into precision-ground, semi-ground, and unground designs. NICE is now part of RBC Bearings.
More than a century after its founding, NICE continues to offer standard inch-dimension radial, angular-contact, and thrust ball-bearing products.
Among its most recognizable families is the NICE 1600 Series.
RBC describes the NICE 1600 Series as precision-ground radial ball bearings manufactured in inch dimensions and intended as a cost-effective precision solution for medium-load applications.
The bearings use retainers to reduce ball-to-ball contact friction and increase allowable operating speed compared with full-complement arrangements. RBC describes the line as recommended for maximum speeds generally in the 5,000 rpm range, although actual operating suitability must always be evaluated using the individual bearing specification and application conditions.
The series is available in:
For an example of the dimensions:
NICE 1606
3/8" bore × 0.9063" OD × 0.3125" width
NICE 1607
7/16" bore × 0.9063" OD × 0.3125" width
RBC currently lists both with a maximum speed of 5,000 rpm in the referenced product configurations.
There is also a useful clue embedded in many standard NICE 1600 Series numbers.
For example:
1606 → 6/16" = 3/8" bore
1607 → 7/16" bore
That can be useful during identification, but the complete part number and suffix still need to be verified because those additional characters communicate construction and other product details.
In other words:
Use the number as a clue, not an excuse to stop measuring.
Why are all these bearing families still around?
Because replacing an otherwise functional piece of equipment just to convert its bearing positions to metric dimensions usually does not make economic sense.
Legacy inch-dimension bearings can still turn up in:
A machine can remain productive for decades.
During that time, the original equipment manufacturer might disappear. Bearing companies can merge. Brand names can change. Product lines get consolidated. A bearing number stamped into a ring 50 years ago may no longer appear in a current catalog.
But the mounting dimensions remain.
A 1-inch shaft doesn't particularly care what year it is.
And if the rest of the equipment is doing its job, there may be absolutely no reason to redesign it.
That is where bearing identification and cross-referencing become especially valuable.
Imagine pulling an old bearing from a machine.
You clean off the ring and find:
RLS8
A quick search gives you several possible equivalent numbers.
Problem solved?
Maybe.
Before ordering the replacement, there is still homework to do.
A proper bearing cross-reference should consider much more than one number.
Verify:
Bore × Outside Diameter × Width
Do not rely solely on the nominal shaft diameter.
When dealing with legacy bearings, the manufacturer can completely change the meaning of a designation.
As XLS demonstrates, identical letters do not necessarily indicate an identical bearing design.
Is the original bearing:
And how many closures are present?
Suffix conventions also vary by manufacturer, so designations such as ZZ, 2RS, D, DD, PP, and others should not automatically be assumed to communicate identical construction across every brand.
How is the bearing lubricated?
Some open bearings operate inside pumps, gearboxes, or other equipment where lubrication comes from the machine's oil system.
Replacing an open bearing with a grease-packed sealed bearing simply because the dimensions match could fundamentally change the lubrication arrangement.
Look for:
And don't assume a familiar suffix means the same thing across every historical manufacturer.
This is particularly important when dealing with a designation such as XLS, where the manufacturer may determine what the basic bearing construction actually is.
If the application requires a particular internal clearance or precision level, these specifications must also be considered before approving a substitute.
Finally:
What is this bearing actually being asked to do?
Consider:
Two bearings that physically fit into the same space are not automatically equivalent for every application.
If an old bearing lands on your desk with an unfamiliar designation, don't immediately start guessing numbers.
Do a little detective work first.
Even a badly damaged bearing can provide useful dimensional and identification information.
Look at:
Photograph everything before cleaning removes a faint marking that might have mattered.
Use appropriate measuring equipment rather than estimating with a ruler or tape measure.
Pay attention to rings, shields, seals, spacers, and unusual geometry that could affect the measurement.
Look for:
This can be critical.
Sometimes the manufacturer name turns an otherwise meaningless series of letters into a recognizable bearing designation.
Knowing where the bearing came from may help determine what it was designed to do.
Compare the entire set of information, not merely the first number that produces an online match.
The bearing industry has changed enormously since anti-friction bearing manufacturing expanded more than a century ago.
◾ Companies merged.
◾ Brands changed hands.
◾ Standards evolved.
◾Metric dimensions became dominant in modern machine design.
But the machines built around earlier inch-series bearings did not simply vanish.
That is why R, RLS, RMS, LS, MS, LJ, MJ, XLS, NICE 1600, and other inch-dimension bearing designations continue to show up in maintenance departments, repair shops, distributor inquiries, and old equipment today.
Understanding these systems is more than a history lesson.
It is practical knowledge for the people responsible for keeping existing machinery operating.
And perhaps the most important lesson is remarkably simple:
Never let a familiar-looking bearing number replace proper identification.
At Bearing & Drive Systems (BDS), bearing identification and cross-referencing are part of what we do every day. Whether you're holding a current production bearing or a decades-old component with little more than a faded number stamped into the ring, dimensions, manufacturer information, design characteristics, and application details can help lead us toward the right replacement.
Send BDS the manufacturer, complete markings, bore, outside diameter, width, and photos if available.
We'll help you figure out what you've got and where to go from there.
Are inch bearings still manufactured?
Yes. Several inch-dimension bearing families remain available for replacement and current applications, including R, RLS/RMS, and NICE 1600 Series bearings. Availability depends on the size, manufacturer, and configuration.
What is an R Series bearing?
R Series bearings are inch-dimension deep groove radial ball bearings manufactured around fractional-inch dimensions. An R8, for example, has a 1/2-inch bore rather than an 8 mm bore.
What is the difference between RLS and RMS bearings?
RLS and RMS identify light- and medium-section imperial deep groove ball-bearing families. Two bearings may have the same bore but different outside diameters and widths.
What do LS and MS bearing numbers mean?
LS and MS are legacy designations associated with light- and medium-section inch bearings. Their numbering system differs from RLS/RMS and LJ/MJ designations, which is why dimensions should always be verified during cross-referencing.
What is an XLS bearing?
XLS does not have one universal meaning across every manufacturer. Fafnir/Timken has used XLS for extra-large inch-dimension radial ball bearings, while MRC has used XLS for an inch-size angular-contact design. The original manufacturer should therefore be identified before selecting a replacement.
What are NICE 1600 Series bearings?
NICE 1600 Series bearings are precision-ground radial ball bearings manufactured in inch dimensions. They are available in open, shielded, and sealed configurations and remain part of the NICE product line.
How do I identify an unknown inch bearing?
Start by recording the manufacturer and all markings, then measure the bore, outside diameter, and width. Note seals, shields, snap-ring grooves, flanges, extended rings, or other special features before attempting to cross-reference the bearing.
Can I replace an inch bearing with a metric bearing?
Not simply because the dimensions are close. The bore, OD, width, internal design, clearance, closures, load requirements, speed, lubrication, and fit must all be considered. A nearly identical metric bearing may still be unsuitable without modifications to the surrounding equipment.
The technical information and dimensional data presented in this article were verified using manufacturer catalogs, engineering references, and historical bearing standards.
Bearing designations, suffixes, dimensions, internal designs, and interchange practices can vary by manufacturer and product generation. A cross-reference should therefore be verified against the manufacturer's current technical data and the requirements of the specific application before a replacement bearing is selected.
Looking for additional bearing information or trying to identify a hard-to-find part? Explore these resources from Bearing & Drive Systems:
Send BDS the manufacturer, part number, dimensions, and photos if available. Our bearing specialists can help identify, cross-reference, and locate hard-to-find and obsolete bearings. BDS specifically supports distributors with sourcing, engineering services, modifications, repairs, and legacy or unavailable components. [bdsbearing.com]