DW4K is a designation from the inch-series family of airframe-type control ball bearings: DW identifies a double-row, extra-wide construction, the digit is a size code, and the suffix letters identify a catalogue variant. Buyers usually meet it on a replacement list, a worn sample or a cross-reference sheet. This guide explains how DW and KP designations are read in general terms, how to match them by dimensions, and what we need to identify a part. NLHB supplies DW4K-type inch control bearings for industrial and aftermarket use only.
A designation describes geometry, not approval
Prefix, size code and suffix tell you the family, nominal bore and variant. They do not tell you whether a given bearing is approved for any aircraft. Our DW4K-type bearings are industrial and aftermarket products; no airworthiness, installation approval or certification is claimed.
How DW and KP designations are built
Airframe-type control bearings are a group of inch-dimensioned ball bearings designed mainly for oscillating and slow, intermittent motion in linkages, rather than for continuous high-speed rotation. The same designation logic appears in several manufacturers' catalogues, which is why a designation such as DW4K is often used as a common reference. The table shows how the parts of a designation are read in general terms.
| Part of designation | Example | General reading | What to confirm |
|---|---|---|---|
| Prefix | DW, KP, DPP, DSP | Family and construction: extra-wide double-row, single-row radial, double-row standard or self-aligning | The issuing catalogue; prefixes are not standardised across all makers |
| Size code | 4 in DW4K | Nominal bore code, commonly in sixteenths of an inch (4/16 = 1/4 in) | Exceptions exist in the smallest sizes; always measure the bore |
| Suffix | K, A, B, X | Catalogue variant: series width, seal or shield, material, plating or internal design | The catalogue definition of the exact suffix; do not assume it from another family |
| Additional marks | Military or NAS part numbers on a drawing | An alternative reference to the same geometry | Used by us only as a source of dimensions, not as a conformity claim |
Designation logic is a starting point, not an identification. Two parts with the same prefix and size code can differ in outside diameter, inner and outer ring width, construction (full complement or caged) and surface treatment. For the wider family overview, see our airframe-type control bearing series guide.
Cross-referencing to RBC and other catalogues by dimensions
Many buyers hold RBC catalogue designations, because RBC Bearings publishes a widely used airframe control bearing catalogue. We cross-reference by dimensions: a designation is translated into bore, outside diameter, ring widths and construction, and those values are compared with our drawing. The result is a dimensionally compatible reference model. It is not a brand authorisation, and it does not make our bearing an approved substitute. RBC is a trademark of its owner and is used here for reference only.
- Take the designation from the customer's list or drawing, including every suffix letter.
- Obtain the dimensions from the issuing catalogue or the customer's drawing: bore d, outside diameter D, outer ring width and inner ring width. In many control bearings the inner ring is wider than the outer ring, so both widths must be recorded.
- Record the construction: single or double row, full complement or caged, rigid or self-aligning, shield or seal type.
- Record material and surface requirements: ring and ball material, plating or coating, lubricant.
- Compare with our drawing and state the result as “dimensionally compatible” or “not compatible”, listing any deviation.
What a dimensional match does not cover
| Characteristic | Covered by a dimensional cross-reference? | How it is defined for an order |
|---|---|---|
| Bore, OD, ring widths, chamfers | Yes | Drawing or catalogue values, converted and checked |
| Internal construction and ball complement | Only if stated in the reference | Section drawing or sample teardown |
| Starting and running torque | No | Agreed test method and limit on the drawing |
| Material, plating, lubricant | No | Written specification per order |
| Airworthiness, installation approval, certification | No | Not claimed. Our DW4K-type bearings are supplied for industrial and aftermarket use. |
What NLHB supplies
We produce DW4K-type inch double-row extra-wide control bearings for industrial machinery and the aftermarket. Turning, raceway grinding, superfinishing and assembly are done in our Cixi factory, and dimensions, roundness and raceway profile are checked on our own equipment. We do not supply these bearings as aircraft parts and make no airworthiness or certification claim. NLHB manufactures miniature and deep groove ball bearings up to P4 precision, and double row angular contact bearings and track rollers up to P6.
What to send for identification
- The complete designation as marked or listed, including suffix letters, and the catalogue it comes from.
- A drawing, or a sample with photographs of both faces and the markings.
- Measured bore, outside diameter, outer ring width and inner ring width, stating the instrument used.
- Application: industrial machine type, motion (oscillation angle or rotation), load direction and environment.
- Required material, plating, seal or shield, lubricant and any torque requirement.
Inch dimensions are easily misread as nearby metric sizes. If you are converting measurements yourself, see our guide to inch bearing size conversion, and our bearing size chart for metric series.
Evidence from our workshop
What to send for a quotation
- Full designation with all suffix letters and the source catalogue.
- Drawing or sample, with photographs of the markings.
- Measured d, D, outer and inner ring widths.
- Industrial application, motion and load description.
- Material, plating, lubricant, seal and torque requirements, and quantity.
Frequently Asked Questions
What is a DW4K bearing?
DW4K is an inch-series designation for a double-row, extra-wide control ball bearing of the airframe type. DW is the family, 4 is the size code and K is a catalogue variant suffix.
What does the 4 in DW4K mean?
In these inch control bearing families the digit is commonly read as the nominal bore in sixteenths of an inch, so 4 points to a 1/4 in (6.35 mm) bore. Always confirm by measurement or catalogue.
Is NLHB's DW4K interchangeable with an RBC DW4K?
We cross-reference by dimensions and can supply a dimensionally compatible reference model. This is not a brand authorisation, and interchangeability in a specific assembly must be confirmed by the user.
Can your DW4K-type bearings be installed in aircraft?
No claim is made for aircraft use. Our DW4K-type bearings are supplied for industrial and aftermarket applications, without airworthiness, installation approval or certification.
Can you identify a bearing from a sample without a drawing?
Yes, for dimensional identification. We measure the sample, record construction and markings, and propose a compatible drawing for your confirmation.
Related guides
Published 2026-09-25. Images show our own workshop and representative products. Final dimensions, grades, inspection limits and supply conditions are confirmed against the requested model, drawing and order.