RBCB546DDNFCAirframe Control Ball Bearing to MS27646-46 / SAE-AS7949, Sealed, 2.3125″ Bore x 2.8750″ OD x 0.281″ Wide

Product Description

What this part is

An RBC airframe control ball bearing from the B500DD extra-light torque-tube series, manufactured to military standard MS27646 and SAE-AS7949. Dash number −46. Bore 2.3125 in, outside diameter 2.8750 in, width 0.281 in.

Airframe control bearings are a distinct product family, not general-purpose ball bearings that happen to be on an aircraft. They exist to support flight-control linkages — torque tubes, bellcranks, push-pull rod ends, pulley brackets — where the motion is oscillating rather than continuous, the load is often applied while nearly stationary, and the bearing must be light, thin-sectioned and utterly reliable. Notice the proportions: 2.875 in outside diameter on a 2.3125 in bore is a wall of about a quarter of an inch, and the bearing is only 0.281 in wide. That is a deliberately minimal, weight-critical section.

Decoding the designation

B5 — RBC’s B500 extra-light torque-tube airframe control series.46 — the size code, corresponding to MS27646 dash number −46. RBC’s own table maps B546DD directly to MS27646-46, so the two numbers are the same part read two ways — which is why both belong in the title.DD — PTFE seals. The DD-suffix series is dimensionally interchangeable with the unsealed B500 series, so a sealed bearing can replace an unsealed one in the same envelope.NFC — a factory-specification suffix. RBC’s published table lists bearings by number plus a separate factory specification (its example is B538DD FS464), and we could not resolve NFC against any public RBC specification list. It is reproduced exactly as marked rather than decoded or dropped, because on an aerospace part the full marking is what your paperwork has to match.

Correcting the source data

Two figures on the previous version of this listing were wrong and are corrected here against RBC’s own published table.

Bore was listed as 2.3 in. The published figure is 2.3125 in (2-5/16 in, 58.738 mm). On a bearing with a bore tolerance of ±0.0007 in, quoting the bore to one decimal place is not a rounding convenience — it is short by 0.0125 in, which is roughly eighteen times the tolerance band. Anyone checking fit against a shaft would have been misled.Width was listed as 9/32 in. That is 0.28125 in and it agrees with the published 0.281 in, so the original was right — but it is now stated in decimal form to match the standard and to sit alongside the tolerance.

Published data — all figures from RBC’s own MS27646 table:
Bore (B): 2.3125 in / 58.738 mm, tolerance +0.0010 / −0.0010 inOutside diameter (D): 2.8750 in / 73.025 mm, tolerance +0.0000 / −0.0015 inWidth (W): 0.281 in / 7.14 mm, tolerance +0.000 / −0.005 inInner ring width (H): 0.250 in / 6.35 mm, tolerance +0.000 / −0.005 inDimension E: 2.531 in / 64.29 mmChamfer C: 0.015 in / 0.38 mm at 45°Radial limit load rating: 10,150 lbf / 45,200 NThrust limit load rating: 4,400 lbf / 19,600 NWeight: 0.17 lb / 0.077 kgRows: 1Seals: PTFE, prelubricated for lifeFinish: cadmium plated on all exposed surfaces except the bore and the sealsStandards: MS27646, SAE-AS7949

Why “limit load” is not a dynamic load rating:
This is the specification most likely to be misapplied, because the numbers look like the C and C0 figures on an industrial bearing and they mean something different.

Airframe control bearings are rated by limit load: the maximum load the bearing can carry without permanent deformation that would impair its function. It is a structural, static-style criterion suited to a component that oscillates through a small arc and spends most of its life holding load rather than rotating. An industrial dynamic rating C, by contrast, is a fatigue-life figure referenced to a number of revolutions.

So do not put a 10,150 lbf radial limit load into an L10 life calculation and expect a meaningful answer, and do not compare it directly against a deep groove ball bearing’s C. Note also the ratio: 10,150 lbf radial against only 4,400 lbf thrust. This bearing is built to take load across the linkage, not along the pin. A control installation that loads it axially is loading it on its weak axis.

Note on the cadmium plating and the PTFE seals:
Both are specification, not finish. Cadmium plating is the traditional aerospace corrosion protection for steel airframe hardware and is galvanically compatible with the aluminium structure these bearings mount into — substituting a zinc- or nickel-plated bearing changes that relationship. The bore and seals are deliberately left unplated so that plating thickness does not disturb the bore tolerance. PTFE seals hold the lifetime lubricant in and are chemically inert to hydraulic fluid and de-icing chemicals, which nitrile would not be. RBC also offers this series in CRES 440C stainless with zinc-nickel plating to OEM specification — a different part number and a different corrosion regime.

Quantity and configuration

Seven bearings in stock, sold individually. Seven is a substantial holding on a standard-part aerospace bearing: enough to do a multi-station torque-tube run in one purchase, or to hold real depth against an AOG requirement. Control linkages typically use these in pairs or in sets at each bearing station, so depth is worth more here than a single unit.

Certification note

We are selling this as surplus industrial stock. It is described honestly against RBC’s published MS27646 data, but we are not an aerospace distributor and we make no claim about airworthiness release, traceability paperwork or 8130 certification. If your application is an airworthy installation, that documentation is a requirement and it is not something we can supply. For ground support equipment, tooling, test rigs, simulators, restoration work and industrial use, an MS27646 bearing at this price is a straightforward proposition.

Interchange guidance

Search forms include B546DDNFC, B546DD-NFC, B546DD NFC, B546DD, B546, MS27646-46, MS27646/46, MS2764646, SAE-AS7949. Adjacent sizes in the same B500DD series: B545DD (MS27646-45, 2.0625 in bore), B544DD (MS27646-44, 1.8125 in bore), B543DD (MS27646-43, 1.5625 in bore). The unsealed B546 is dimensionally interchangeable with this sealed build. The related MS27641 series is a different airframe control standard — check the standard number, not just the dash.