Aerospace Bushings: Standard Sleeves, Liners and Bronze
An aerospace bushing is a replaceable sleeve, plain or flanged, pressed into a hole so the pin or bolt wears the bushing instead of the structure. Standard parts come from NAS75 and NAS77, PTFE lined sleeves from SAE AS81934, and custom bronze bushings are often machined from AMS 4640 nickel aluminum bronze.
Updated
Types and where they are used
Bushings protect expensive holes. A lug on a landing gear link, an actuator clevis or a control surface hinge fitting is worth far more than the sleeve in it, so the design puts a bushing in the hole and replaces the bushing when it wears. The type depends on whether the joint moves and how it is lubricated.
| Type | Typical material | Where it is used |
|---|---|---|
| Plain sleeve, press fit (no flange) | Alloy steel, cadmium plated, or CRES | Bolt holes in fittings and lugs to protect against fretting and bearing damage |
| Flanged sleeve | Alloy steel, CRES, bronze | Where the flange takes axial load or sets spacing, and stops migration |
| Self-lubricating lined sleeve, plain or flanged | Metal shell with PTFE liner in the bore | Oscillating pins where grease access is poor |
| Bronze bearing bushing | Nickel aluminum bronze, aluminum bronze | Greased pivots, landing gear and actuator joints |
| Custom machined bushing | Per drawing | Repairs, oversize replacements, special fits |
If the joint needs misalignment as well as rotation, it wants a spherical bearing instead; see spherical bearings and rod ends. Rolling element bearings are on aerospace bearings.
The specifications that govern bushings
Standard bushings are bought by National Aerospace Standard part number; lined bushings by SAE AS81934; and custom bronze bushings by the drawing, with the bar stock bought to an AMS material spec.
| Document | What it covers | Status as verified |
|---|---|---|
| NAS75 | Bushing, plain, press fit; listings describe a solid sleeve with no outside flange in 4130 or 8630 steel, cadmium plated | NAS standard, CAGE 80205 as design holder (Boeing Distribution listings); check the sheet revision |
| NAS77 | Sleeve bushings with material letter variants; listings show alloy steel, aluminum and copper alloy versions | NAS standard in active distribution; one listing titles a NAS77 size as flanged, so confirm configuration on the sheet |
| SAE AS81934 | Sleeve bearings, plain and flanged, self-lubricating with PTFE liner in the bore, -65 to 325 F | AS81934C revised September 2019 (SAE) |
| SAE AMS 4640 | C63000 nickel aluminum bronze bars, rods, shapes, tubes and forgings, drawn and stress relieved (HR50) or temper annealed (TQ50) | AMS 4640H is the current revision (National Bronze) |
| QQ-C-465 | Federal specification for aluminum bronze, cited on a NAS77 copper alloy listing alongside AMS 4640 | Shown as a material response on a distributor listing; confirm status before use |
AS81934C is worth reading if you buy lined bushings in volume. SAE's summary says Revision C updated the high and sub-zero temperature test methods, added room temperature break-in cycles, added qualification requirements for CRES substrates, tightened test pin and housing tolerances and added fluid contaminants including a specified anti-icing fluid.
Have a part like this?Send it in under a minute. A person replies within 1 business day.How the part number is built: NAS75
NAS75 part numbers read NAS75 plus a bore code plus a length code. We could not obtain the NAS sheet itself, so the decode below comes from distributor technical listings, and the exceptions are noted.
| Example | Bore (listed) | Length (listed) | Reading |
|---|---|---|---|
| NAS75-4-010 | 0.2500 to 0.2515 in | 5/16 in | -4 is a 1/4 in bolt (4/16); -010 is 10/32 in |
| NAS75-4-006 | 1/4 in nominal | 0.1825 to 0.1875 in | -006 is 6/32 in |
| NAS75-7-015 | 0.4375 to 0.4390 in | 0.4638 to 0.4688 in | -7 is 7/16 in; -015 is 15/32 in |
| NAS75-10-100 | 0.6250 to 0.6265 in | 0.9950 to 1.0000 in | -10 is 5/8 in; the length code does not follow the 32nds rule here |
So the middle number is the nominal bore in sixteenths, and the last number is usually the length in thirty-seconds, with exceptions. Never build a NAS part number from the pattern; take it from the sheet or the drawing. NAS77 adds a material letter after the base number in listings, such as NAS77A3-025, which one distributor shows as copper alloy 642 or 630 to QQ-C-465 or AMS 4640, with a 0.1900 to 0.1915 in bore and 0.302 to 0.317 in length.
Materials, finishes and the trade-offs
Pick the bushing material for the job the bushing does: steel to protect a static bolt hole, bronze for a greased pivot, a PTFE liner where grease cannot reach, and CRES where plating is unwelcome.
- Alloy steel, cadmium plated. The usual NAS75 construction. Hard and stiff, good against fretting in clamped joints. Cadmium is under regulatory pressure and listings carry Proposition 65 warnings, so some programs move to alternative platings by drawing change.
- Nickel aluminum bronze to AMS 4640. Published composition limits are roughly 9 to 11 percent aluminum, 2 to 4 percent iron and 4 to 5.5 percent nickel, balance copper. Suppliers list landing gear bushings among its uses. It runs well against hardened steel pins with grease and resists corrosion, but against aluminum structure it is a dissimilar metal couple.
- PTFE lined, AS81934. No grease, low friction, good for small oscillations. Temperature is capped at 325 F by the spec range, and Revision C added fluid contaminant testing, a reminder that liners care what they are exposed to; protect them during painting and cleaning.
- CRES. Corrosion resistant without plating; watch galling against CRES pins.
Galvanic and stress corrosion both matter when a bushing goes into aluminum. NASA MSFC-STD-3029, discussed on our aluminum alloys page, lists interference-fit bushings as a source of sustained tensile stress that drives stress corrosion in susceptible tempers. For copper alloys and steels in general see materials, and for plating and primer options see surface finishing.
Interference fits and installation
Most bushings are retained by interference: the bushing OD is larger than the hole, so it has to be pressed or shrunk in. The fit, the method and any post-install machining belong on the drawing or the repair manual, not left to the installer.
- Press fit. The bushing is pressed straight with a piloted tool. A lead-in chamfer on hole and bushing prevents shaving, and many drawings require wet installation with primer or sealant to block galvanic corrosion.
- Shrink or freeze fit. Chilling the bushing, or warming the housing where the material allows it, reduces the force needed and limits scoring of the bore. Plan for condensation on chilled parts, and keep the wet sealant requirement.
- Final sizing. Pressing a bushing in closes up its bore. Drawings often call for reaming or honing after installation to bring the ID to size and position. Lined bushings are not reamed through the liner unless the manufacturer allows it.
- Retention. Flanged bushings stop axial walk in one direction; some designs add staking, swaging or a retaining feature for the other.
Excess interference is a design risk as well as an installation problem, because it leaves sustained hoop stress in the lug. That is a stress engineer's call, and it is why a part number change to a different OD or material is not a buyer's decision.
Wear and replacement
Bushings are consumables. Maintenance manuals set wear limits on ID, ovality and play, and replacement is normally the same part number. When a hole has been damaged by a worn or migrated bushing, repair schemes often call for an oversize OD bushing machined to the drawing after the hole is cleaned up. Those custom bushings are where sourcing and machining meet: the bronze or steel bar has to be bought to the right AMS spec with certs, the bushing machined to tight OD tolerance and finished, and the paperwork tied to the repair. We can source the bar, machine the bushing and deliver it with an AS9102 first article when the program needs one; see aerospace CNC machining.
Ordering checklist for the PO
- Full NAS or AS part number with every letter and dash, and the sheet or spec revision (NAS75, NAS77, AS81934 slash sheet).
- For custom bushings: drawing number and revision, bar material spec and temper (for example AMS 4640 HR50 or TQ50), finish and any post-install machining allowance.
- Plating and finish called out by spec, or the alternative to cadmium your program approved.
- Manufacturer and lot traceability, certificate of conformance, and mill certs for bar stock. See material certs and traceability.
- DFARS specialty metals when steel or nickel bearing alloys go into a DoD end item; see DFARS specialty metals.
- Packaging that protects OD finish and liners: individually bagged or tubed, no nesting of bushings against each other.
Counterfeit and quality risks, and how to receive bushings
The risk with bushings is less outright counterfeiting than wrong material and lost traceability. A cadmium plated steel sleeve and a zinc plated one look alike; a bronze bushing turned from unknown bar looks the same as one from AMS 4640 stock. Lined bushings can carry an unqualified liner. Buy standard parts from the manufacturer or authorized distribution, and apply SAE AS6174 controls and our counterfeit parts avoidance process to anything else.
At receiving, measure OD and ID against the sheet with calibrated gages, since OD controls the interference; check flange dimensions and chamfers; check plating appearance; and confirm the cert ties the lot to the material spec. For bronze, a handheld XRF check is a quick way to confirm the alloy family. See receiving inspection and inspection and metrology.
How we source bushings
We do not stock bushings or list prices, and we are not an authorized distributor for any maker. We source standard NAS and AS bushings through authorized distribution or the manufacturer with lot traceability, and we have custom bushings machined from certified bar by qualified shops, with your drawing requirements flowed down. Both can ride on one PO with the fittings, links and fasteners they go into, or be kitted by assembly. For superseded or hard to find bushing part numbers, our obsolete parts process looks for authorized stock first and then a made-to-print replacement your engineering approves. Browse the motion category or the parts index.
Get bushings sourced or made to print
Send the NAS or AS numbers, or the drawing for custom bushings, with quantity, material spec and any installation or FAI requirement. Request a quote for bushings, and add the mating parts so they arrive together.
Send the job. A person replies within 1 business day.
Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.
We have it.
Reference . A person replies within 1 business day. Watch for our email from [email protected].
Questions
What is the difference between NAS75 and NAS77 bushings?
Distributor listings describe NAS75 as a plain press fit sleeve with no outside flange, usually 4130 or 8630 steel with cadmium plate. NAS77 listings show sleeve bushings with material letter variants, including aluminum and copper alloy versions, and at least one listing titles a NAS77 size as flanged. Read the current NAS sheet for configuration before substituting one for the other.
What is AMS 4640 used for?
AMS 4640 covers C63000 nickel aluminum bronze in bars, rods, shapes, tubes and forgings, supplied drawn and stress relieved (HR50) or temper annealed (TQ50). Suppliers list landing gear bushings, valve stems, pump shafts and gears among its uses. AMS 4640H is described by National Bronze as the current revision. Name the temper on the PO, because the two conditions differ in strength.
What temperature can a PTFE lined bushing take?
SAE AS81934, the general specification for self-lubricating plain and flanged sleeve bearings with a PTFE liner in the bore, covers -65 F to +325 F. Revision C, issued in 2019, updated the high and sub-zero temperature test methods. Above that range, a metal bushing with grease or a special high temperature liner approved by engineering is the usual answer.
Should bushings be installed wet?
Follow the drawing or repair manual, but many aerospace drawings do require wet installation with primer or sealant, particularly when a steel or bronze bushing goes into aluminum. The sealant fills the interface and slows galvanic corrosion between dissimilar metals. Installing dry when the drawing says wet is a nonconformance even if the fit is correct.
Why does a bushing need reaming after it is pressed in?
An interference fit squeezes the bushing, so its bore shrinks during installation. To hold the final ID size and position relative to other holes, drawings often leave a small allowance and call for reaming or honing after installation. Lined bushings are an exception, since cutting the liner can ruin it, so check the manufacturer guidance first.
Can I build a NAS75 part number from the bore and length?
No. Listings suggest the middle number is the bore in sixteenths and the last number is usually the length in thirty-seconds, but NAS75-10-100 does not follow the length rule. Take the part number from the drawing or the NAS sheet, and have the source confirm dimensions against the current revision before you order.
Related
Sources
- Boeing Distribution: NAS75-4-020 bushing, sleeve
- Military Fasteners: NAS75-10-100 sleeve bushing
- Military Fasteners: NAS75-4-010 sleeve bushing
- Military Fasteners: NAS77A3-025 sleeve bushing
- SAE: AS81934C sleeve bearings, plain and flanged, self-lubricating
- National Bronze: AMS 4640 C63000 nickel aluminum bronze
- National Bronze: what is AMS 4640H
- Aircraft Materials: nickel aluminium bronze AMS 4640
- NASA MSFC-STD-3029A, stress corrosion guidelines
Ready to
source it?
A person replies within 1 business day. NDA first.
Request a quote