Spherical Plain Bearings and Rod Ends for Aerospace
A spherical plain bearing is a ball swaged inside an outer race that allows misalignment under load; a rod end puts that joint on a threaded shank. Aerospace versions are governed by SAE general specs such as AS81820 and AS8942 for PTFE lined bearings, AS81936 and AS8976 for metal-to-metal, and AS81935 for self-lubricating rod ends.
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Types and where they are used
Plain spherical bearings carry high loads at low speed through oscillation and misalignment, which is why they sit at actuator ends, landing gear links, flight control rods, engine mounts and door and hatch hinges. They differ from airframe ball bearings in that nothing rolls: the ball slides against a liner or a metal race. The choice between liner and metal contact drives most of the buying decisions.
| Type | How it works | Where it is used |
|---|---|---|
| Self-lubricating spherical, PTFE lined | Woven or molded PTFE liner bonded in the outer race; no grease | Control linkages and actuator ends where maintenance access is poor |
| Metal-to-metal spherical | Steel, CRES or copper beryllium ball in a metal race, greased through grooves and holes | High load or high temperature joints with a lube schedule |
| Self-lubricating rod end | PTFE lined spherical insert in a threaded body, male or female thread | Push pull rods and adjustable links |
| Ball bearing rod end | Antifriction ball bearing in a rod end body | Low friction control rods; covered by AS6039 and AS21150, not the plain bearing specs |
| Lined bore and wide series | Liner also in the bore, or a wider ball for more capacity | Joints with rotation on the pin as well as misalignment |
Rolling element airframe bearings are covered on our aerospace bearings page, and plain sleeves on bushings.
The specifications that govern spherical bearings and rod ends
Most current documents are SAE AS standards that replaced military specifications and MS sheets. The detail part numbers on drawings still often carry the MS or M prefix, so expect to see both.
| Document | What it covers | Status as verified |
|---|---|---|
| SAE AS81820 | Self-lubricating spherical plain bearings and liner qualification; slash sheets such as M81820/1 to /4 | Current SAE spec that replaced MIL-B-81820 (RBC) |
| SAE AS14101 | Plain, self-lubricating, self-aligning, low speed, narrow bearing with grooved race, -65 to 325 F | AS14101E (2018) listed as most recent (ANSI); MS14101 cancelled and superseded by AS14101 (EverySpec) |
| SAE AS8942 | Plain and PTFE lined self-aligning bearings, -65 to 250 F | AS8942A revised February 2022 (SAE) |
| SAE AS81936 | Self-aligning plain bearings with copper beryllium ball and CRES race, -65 to 350 F | AS81936A (2006); QPL-AS81936 maintained |
| SAE AS8976 | All metal self-aligning plain bearings: alloy steel, aluminum bronze or all CRES | AS8976A revised February 2012; MIL-B-8976 cancelled |
| SAE AS81935 | Self-aligning, self-lubricating plain rod ends with PTFE liner, -65 to 325 F | AS81935C revised June 2011 (SAE) |
| SAE AS21150 | Ball rod end, double row, precision, solid shank, self-aligning, airframe | AS21150F (June 2022) current; MS21150 cancelled (EverySpec) |
| SAE AS6039 | General spec for ball bearing rod ends (formerly MIL-B-6039) | Cited as current by RBC |
Note the trap in the last two rows. MS21150 is often grouped with plain rod ends in conversation, but RBC lists it under AS6039 as a solid shank ball bearing rod end. If the drawing calls MS21150 or AS21150, you are buying an antifriction bearing with grease, not a PTFE lined plain rod end, and the substitution rules differ.
Have a part like this?Send it in under a minute. A person replies within 1 business day.How the part number is built: MS14101-5 and the M81935 sheets
On the narrow self-lubricating sheets, the dash number tracks the bore in sixteenths of an inch. A distributor technical listing for MS14101-5 shows how much the short number carries.
| Element | Meaning |
|---|---|
| MS14101 | Plain, self-lubricating, self-aligning, low speed, narrow, grooved outer ring; now SAE AS14101 |
| -5 | Bore 0.3120 to 0.3125 in (5/16 nominal) |
| Outer ring | OD 0.7495 to 0.7500 in, width 0.276 to 0.286 in, 17-4 PH (composition 630) to AMS 5643 |
| Ball | Width 0.373 to 0.375 in |
| Retention | Staking groove in the outer ring face, groove center diameter 0.662 in |
| Rating | Static radial load rating 8,750 lb |
Boeing Distribution listings confirm the pattern at the ends of the range: MS14101-3 has a 0.1895 to 0.1900 in bore for a No. 10 bolt, and MS14101-8 a 0.4995 to 0.5000 in bore.
Self-lubricating rod ends use AS81935 slash sheets, where the sheet number encodes width, thread and material. RBC's published list:
| Sheet | Series | Thread | Body material |
|---|---|---|---|
| M81935/1, /2 | Wide, high capacity | External, internal | Alloy steel |
| M81935/4, /5 | Narrow, light capacity | External, internal | Alloy steel |
| M81935/6, /7 | Wide, high capacity | External, internal | CRES PH13-8Mo |
| M81935/8, /9 | Narrow, light capacity | External, internal | CRES PH13-8Mo |
The dash number after the sheet then sets size and thread. Do not assume dash numbers line up across sheets; read the sheet.
Materials, liners and the trade-offs
Liner bearings trade some temperature range for zero maintenance; metal-to-metal bearings take heat and abuse but need grease on a schedule. The temperature limits in the general specs make the difference concrete: AS8942 lined bearings are rated to 250 F, AS81935 rod ends and AS14101 bearings to 325 F, and AS81936 copper beryllium on CRES to 350 F.
- PTFE liners. The liner is the bearing surface, so liner qualification matters more than the race. RBC states it makes four liner materials qualified to AS81820 and over 60 other self-lubricating materials for specific needs, and that high temperature liners exist for turbine engine use. A liner swap is a part number change.
- Race materials. 17-4 PH, PH13-8Mo and 440C stainless resist corrosion without plating. Alloy steel bodies are plated, and cadmium is common on legacy parts.
- Copper beryllium balls. AS81936 pairs a Cu-Be ball with a CRES race for galling resistance in metal contact. Beryllium dust is a recognized health hazard, so leave any rework of these parts to the manufacturer.
- Aluminum bronze. AS8976 covers alloy steel, aluminum bronze and all CRES constructions, and RBC offers its MS21154 and MS21155 narrow series in alloy steel or aluminum bronze.
- Galvanic contact. A CRES or bronze outer race staked into an aluminum housing is a dissimilar metal joint. Drawings usually call for a finish or sealant on the housing bore; follow it. See aluminum alloys for the stress corrosion side of pressing parts into aluminum.
Installation: staking and swaging
Most aerospace sphericals are retained by deforming a lip on the outer race into a chamfer in the housing, called staking. The bearing manufacturer's procedure, the groove size and the axial retention test define a good installation.
NHBB's published staking procedure is a useful reference. The anvils are tool steel heat treated to Rc 55 to 60. Staking force is the bearing OD times a constant for the groove size: 7,700, 12,000, 17,700 and 25,800 lb per inch of OD for grooves A through D, based on 140,000 psi outer race material and scaled with tensile strength. Force is set by a trial assembly for each new bearing lot, excessive force is avoided because it distorts the bearing, and at minimum the first and last staked articles are axial proof tested. A slight gap between race lip and housing chamfer is acceptable if the bearing meets its thrust load.
Roller swaging is the alternative: rollers form the lip progressively instead of one anvil stroke. A 2021 finite element study of self-lubricating spherical bearings found that more swaging time, load and roller speed raised push-out load, but excessive load and speed increased radial displacement and reduced rotational freedom. Minebea Mitsumi's catalog adds that a gap up to 0.15 mm after staking does not affect axial capacity and that excessive staking pressure shortens bearing life.
For the buyer, this means staking tools, force and proof load are part of the installation spec, and the bearing lot should be traceable to the trial that set the force. When we source a machined housing with the bearing installed, those requirements go to the shop on the PO.
Load ratings
Sheets for plain spherical bearings tabulate static radial load ratings, such as the 8,750 lb on MS14101-5; that is a static capability, not a wear life. Oscillating life under load depends on the liner and comes from the manufacturer's and the specification's test data, so ask for it rather than estimating it from the static number. For ball bearing rod ends, RBC states the limit load rating follows K n d squared with K about 3,200, and never exceeds two thirds of minimum static fracture strength. Compare like with like: a wide series insert carries more than a narrow one of the same bore, which is why RBC labels them high capacity and light capacity.
Ordering checklist for the PO
- Full part number with sheet and dash number, and the controlling SAE spec at its revision (AS81820, AS14101, AS8942, AS81936, AS8976, AS81935, AS21150).
- QPL source where the spec has a qualified products list, such as QPL-AS81936; name the qualified manufacturer if your drawing does.
- Liner identity for lined bearings, and race and body material, with plating.
- Manufacturer and lot traceability, certificate of conformance, and material certs when required. See material certs and traceability.
- DFARS specialty metals for DoD end items; steels, CRES and nickel alloys are covered. See DFARS specialty metals.
- Installation requirements if we are buying the bearing installed: staking or swaging method, groove, proof load, and inspection.
- Packaging: individually bagged and labeled, with no lubricant added to PTFE lined parts.
Counterfeit and quality risks, and how to receive them
Lined bearings are vulnerable because the liner is invisible once the ball is swaged in. A bearing with an unqualified liner looks identical and fails early in service. Metal parts can also be remarked with a different sheet number to fill an order. Treat any non-authorized source under SAE AS6174 counterfeit materiel controls and our counterfeit parts avoidance process.
At receiving, check that marking matches the sheet and dash number, measure bore, OD and width against the sheet, confirm the staking groove is present where the sheet calls one, and check that the ball moves smoothly without binding or visible play against the manufacturer's acceptance criteria. Confirm lot numbers match the cert. Do not wash or lubricate PTFE lined parts. Our receiving inspection guide covers holds and MRB.
How we source spherical bearings and rod ends
We do not hold inventory or claim to represent any bearing maker. We source sphericals and rod ends through authorized and franchised distributors or the manufacturer, with lot traceability and the manufacturer's certs flowed through to you, and we can put them on the same PO as the machined clevis, lug or link they go into, or deliver them installed by a shop working to your staking spec. For superseded MS numbers and out of production liners, we look for remaining authorized stock first and then for alternates your engineering approves, as described under obsolete aerospace parts. Browse the motion category or the full parts index.
Send the bearing list
Send the MS, M or AS part numbers, the spec revisions, quantity and whether you need them loose, kitted or installed. We return a source, a lead time and the paperwork you will receive. Request a quote for sphericals and rod ends.
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Questions
What replaced MS14101?
EverySpec lists MS14101J as cancelled and superseded by SAE AS14101, and the ANSI webstore lists AS14101E from 2018 as the most recent edition. The bearing is a plain, self-lubricating, self-aligning, low speed, narrow bearing with a grooved race rated -65 to 325 F. Distributors still sell parts under MS14101 dash numbers, so state the AS revision on the PO.
Is MS21150 a plain rod end or a ball bearing rod end?
It is a ball bearing rod end. RBC lists MS21150 as its REP-S solid shank rod end under SAE AS6039, and the successor SAE AS21150F describes a double row precision ball rod end. It is grease lubricated, unlike PTFE lined plain rod ends to AS81935, so do not treat the two as substitutes without engineering approval.
Should I choose a PTFE lined or a metal-to-metal spherical bearing?
Choose lined when you want no grease and the temperature is within the liner rating, for example 250 F under AS8942 or 325 F under AS81935 and AS14101. Choose metal-to-metal, such as AS81936 copper beryllium on CRES at up to 350 F, when the joint is greased on a schedule, runs hotter or sees heavy shock loads. The drawing normally settles it.
How much force does it take to stake a spherical bearing?
It depends on the groove and the bearing OD. NHBB publishes 7,700, 12,000, 17,700 and 25,800 lb per inch of OD for grooves A through D, based on 140,000 psi race material. The force is confirmed by a trial assembly for each bearing lot, and the first and last staked parts are proof tested for axial retention.
Can I reuse a staked bearing after removal?
Treat removed staked bearings as scrap unless the manufacturer or the repair manual says otherwise. Removal pushes the formed lip back through the housing chamfer and can distort the race and damage the liner. The housing chamfer may also need inspection or repair before a new bearing is staked in.
Do the M81935 slash sheets mean different materials?
Yes. In RBC's list, M81935/1, /2, /4 and /5 are alloy steel bodies, and /6 through /9 are CRES PH13-8Mo. Odd and even sheets split wide high capacity and narrow light capacity versions with external or internal threads. Order the exact sheet; a CRES rod end is not an automatic replacement for alloy steel.
Related
Sources
- RBC Bearings: spherical plain bearings engineering
- RBC Bearings: rod end plain bearings engineering
- SAE: AS81935 rod end bearings, self-lubricating
- EverySpec: MS14101J cancelled, superseded by SAE AS14101
- Military Fasteners: MS14101-5 technical data
- SAE: AS8942A plain and PTFE lined self-aligning bearings
- SAE: AS81936 Cu-Be ball, CRES race bearings
- SAE: AS8976A all metal self-aligning bearings
- EverySpec: MS21150D status
- NHBB: rod end and spherical bearing staking procedures
- Springer: roller swaging and push-out of self-lubricating spherical plain bearings (2021)
- MinebeaMitsumi: rod end and spherical bearing installation
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