Panel Fasteners, Safety Wire and Safety Cable
Quarter-turn panel fasteners hold access panels and cowls; nonstructural ones were bought to MIL-F-5591, now NASM5591, with a qualified products list, and Dzus control panel fasteners to MIL-F-25173. Safety wire is NASM20995 (formerly MS20995), installed per NASM33540 or SAE AS567, and safety cable kits are bought to SAE AS4536.
Updated
Panel fastener types and where they are used
Panel fasteners are captive: the stud stays in the panel when it is unlocked, so nothing falls into the airframe. The FAA General handbook groups them as turn lock fasteners, also called quick opening or stressed panel fasteners, and names Dzus, Camloc and Airloc as the most common families. These are trade names; MIL and NASM documents describe the generic product.
| Family | Parts | Where used | Identification |
|---|---|---|---|
| Dzus type | Stud, grommet, spring receptacle | Inspection plates, doors, removable panels | Head marked with head style, diameter in sixteenths of an inch and length in hundredths |
| Camloc type | Stud assembly, grommet, rigid or floating receptacle | Cowlings and fairings; a heavy-duty line for stressed panels that carry load | Series numbers in the maker's catalog |
| Airloc type | Stud, cross pin, rigid or floating receptacle | Access panels | Grip stamped on the stud head in thousandths of an inch |
In the handbook's Dzus example, a stud marked F 6 1/2 0.50 is a flush head stud with a body diameter of 6 1/2 sixteenths of an inch and a length of 0.50 inch, measured from the head to the bottom of the spring hole. Dzus studs come in wing, flush and oval heads, lock with a quarter turn clockwise and release counterclockwise. Airloc receptacles are classified No. 2, No. 5 and No. 7 by rivet hole spacing of 3/4, 1 and 1 3/8 inch, and the Airloc cross pin must never be reused once removed.
The panel fastener specifications
| Document | What it covers | Status as listed on EverySpec, October 2026 |
|---|---|---|
| MIL-F-5591C | Fasteners, panel, nonstructural, for internal or external aircraft parts | Cancelled, superseded by NASM5591 |
| MIL-F-25173A | Fastener (Dzus), control panel, aircraft equipment, dated 16 February 1956 | Reactivated by Notice 2 of 10 April 2001 for new or existing design; listed active |
MIL-F-5591C, as published, shows how much a panel fastener spec controls:
- Classification: Type I flush head, Type II oval head, Type III wing head; Class A floating receptacle and Class B rigid receptacle; Styles 1 to 3 for stud and receptacle or stud, grommet and receptacle designs and dimple depth.
- Qualification: fasteners had to be qualified for listing on the applicable qualified products list. Ask whether NASM5591 or your drawing still requires a qualified source.
- Function: the stud must engage within 180 degrees of clockwise rotation, lock positively within 85 to 135 degrees after engagement with a positive stop, and release within 85 to 135 degrees counterclockwise. Flush heads must sit within 0.015 inch of the panel.
- Finish: aluminum parts anodized per MIL-A-8625; steel and copper alloy parts cadmium plated per QQ-P-416 Type II Class 2.
- Testing: locking torque, tension, shear, vibration and salt spray.
- Interchangeability: parts with the same manufacturer's part number must be fully interchangeable.
Many current designs call a manufacturer's part number instead of a MIL or NASM number. In that case the manufacturer's drawing is the spec, and substitution of another brand needs engineering approval even if the fastener looks the same.
Have a part like this?Send it in under a minute. A person replies within 1 business day.Receptacles and how panel fasteners are installed
The receptacle is riveted to the structure and the stud and grommet go in the removable panel. The handbook notes that Camloc studs and grommets go into plain, dimpled, countersunk or counterbored holes depending on location and panel thickness, and that floating receptacles allow for misalignment. Panel thickness drives stud length, so the buyer needs the total grip, including any paint or sealant buildup, before ordering. For Airloc fasteners the handbook says the total material thickness must be known before the correct stud is selected.
Receptacles are usually riveted with small solid rivets, so a panel fastener kit often includes rivets of the size the receptacle drawing calls. Grommets on Dzus fasteners are aluminum; springs and studs are cadmium plated steel in the handbook's description.
Safety wire and safety cable specifications
| Document | What it covers | Status |
|---|---|---|
| MS20995E | Wire, safety or lock, superseding AN995 | Cancelled, superseded by NASM20995 (EverySpec) |
| MS33540J | Safety wiring and cotter pinning, general practices for | Cancelled, superseded by NASM33540 (EverySpec) |
| SAE AS567L | Safety cable, safety wire, key washers and cotter pins for propulsion systems, general practices for use of | Revised 10 September 2021 (SAE Mobilus) |
| SAE AS4536 | Safety cable kit procurement specification and requirements for use | Issued January 1993; AS4536D listed as latest (SAE Mobilus) |
| FAA AC 43.13-1B | Acceptable methods for safetying in maintenance and repair | Current FAA advisory circular with Change 1 |
SAE describes AS4536 as covering aircraft-quality safety cable kits of cable and ferrules in UNS S30400 (AMS 5697), UNS S32100 (AMS 5689) and UNS N06600 (AMS 5687), and says it also specifies installation practices. Order safety cable to AS4536 with the cable size the drawing calls; the kit and its tool are matched by size. One cable maker lists cable and ferrules in 0.032, 0.040 and 0.062 sizes.
Safety wire materials and sizes
Safety wire is chosen by hole size, temperature, corrosion and whether the wire must break on purpose. AC 43.13-1B and SAE AS567, as summarized in public references, give the main choices:
- Stainless steel is the default lockwire. Aircraft Spruce lists its MS20995 wire as Type 302/304 stainless, soft temper, in 0.020 to 0.051 inch sizes.
- Monel and Inconel are listed for turnbuckle lockwire by AC 43.13-1B, and public summaries of SAE AS567 cite them for high temperature work.
- Carbon steel and aluminum alloy wire are also allowed for turnbuckles by AC 43.13-1B. The AC cautions not to confuse steel with aluminum wire.
- Copper or brass, 0.020 inch only, is required as shear wire on some emergency devices, and copper (0.020) or aluminum (0.031) wire is used as a seal on first-aid kits, extinguishers, emergency valves and oxygen regulators.
AC 43.13-1B also says not to use stainless, Monel, carbon steel or aluminum alloy wire to secure emergency mechanisms such as exit handle guards and fire extinguishers, where the wire must break.
Size rules from AC 43.13-1B
- Double-twist method: 0.032 inch minimum wire on parts with holes larger than 0.045 inch.
- 0.020 inch double strand may be used on holes between 0.045 and 0.062 inch with parts spaced less than 2 inches apart.
- Single-wire method: use the largest wire the hole will take.
Lockwire procedures at a high level
Safety wire does not create or hold torque; AC 43.13-1B defines safetying as preventing disengagement under vibration. The procedure points that affect buying and receiving:
- Two methods. Double twist is most common; single wire is for closely spaced groups in a closed pattern, electrical parts and hard to reach places.
- Tension in the tightening direction. The wire is routed so that if one fastener starts to loosen, the pull tightens it.
- Group limits. The FAA General handbook says widely spaced bolts by the double twist method are limited to a group of three in series, and closely spaced bolts to what a 24-inch length of wire can reach.
- Torque first. Never overtorque or back off a fastener to align holes; use a different bolt or washer instead.
- Finish. Leave four to six turns (about 1/2 to 5/8 inch) of pigtail after the loop, bent under toward the part, with no nicks or kinks. Wire is pulled taut but not overstressed.
- Single use. Wire is cut off, never twisted off, and not reused.
Safety cable replaces the twist with a crimped ferrule applied by a tensioning tool. The tool maker describes threading the cable, tensioning, crimping the ferrule and cutting the excess, and claims faster installation and fewer sharp ends than lockwire. AS4536 sets the requirements for use, so programs adopting cable should write it into their process and train installers on the tool.
What to put on the PO
- Panel fasteners: full stud, grommet and receptacle part numbers as a set, the governing spec (NASM5591, MIL-F-25173 or the manufacturer's drawing) and revision, total grip, receptacle class (floating or rigid), and whether a qualified source is required.
- Safety wire: NASM20995 part number with material and diameter, and the spool size you want.
- Safety cable: AS4536 kit part numbers with cable size and material, ferrules, and the matched installation tool and any calibration requirement.
- Manufacturer and lot traceability on every item, with a certificate of conformance.
- Finish restrictions: cadmium appears in the older specs; state if your program prohibits it.
- DFARS specialty metals where the contract carries 252.225-7009: stainless, Monel and Inconel wire and steel studs are covered metals. See DFARS specialty metals.
- Packaging: wire on labeled spools by material and size; fastener sets bagged by assembly.
Counterfeit and quality risks, and how to receive them
The risks are look-alike panel fasteners from an unapproved source and wire of the wrong alloy. AS6174 covers counterfeit materiel of any type.
- Panel fasteners: confirm the manufacturer's part number and markings, and on a sample check that the stud engages, locks and releases within the quarter turn.
- Safety wire: verify diameter with a micrometer and alloy with the cert. Aluminum wire mistaken for steel is the specific hazard AC 43.13-1B warns about; copper shear wire in a structural location is the reverse error.
- Safety cable: check the ferrule and cable size against the tool nose and the kit number; mixed sizes will crimp poorly.
- Reject unlabeled spools and loose fasteners without lot identity.
See receiving inspection and counterfeit parts avoidance.
How we source panel fasteners and lockwire
We do not stock these parts, publish prices or claim to be an authorized distributor for any brand. We source through authorized and franchised distributors or the manufacturer, flow down your spec and cert requirements, and check markings and paperwork before shipment. Panel fasteners usually go with fabricated panels, so we can put them on one PO with sheet metal fabrication or ground support equipment and have receptacles installed by the shop. We also kit lockwire and cable with the drilled bolts, castellated nuts and cotter and clevis pins for an assembly. Discontinued panel fastener series go through our obsolete parts service. Related: threaded inserts, surface finishing, stainless steels, nickel superalloys for Inconel wire, and the fasteners hub.
Get panel fasteners and lockwire sourced
Send the stud, grommet and receptacle numbers, wire or cable specs and quantities through a hardware quote request. A person replies within one business day, and when the fasteners ride with panels or GSE we quote everything on one PO with one lead time. Every order ships with a certificate of conformance.
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.
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Questions
What replaced MS20995 safety wire?
NASM20995. EverySpec lists MS20995E, Wire, Safety or Lock, which itself superseded AN995, as superseded by NASM20995. The part number style carried over, so distributors still sell wire under MS20995 numbers. On new POs cite NASM20995 and its revision, the material and the diameter, and install it per NASM33540 or SAE AS567 as your program requires.
What diameter safety wire should I use?
AC 43.13-1B says to use 0.032 inch minimum wire for the double-twist method on parts with holes larger than 0.045 inch. Wire of 0.020 inch, double strand, may be used on holes between 0.045 and 0.062 inch with parts less than 2 inches apart. With the single-wire method, use the largest wire the hole accepts. Shear and seal wire are separate cases.
Is safety cable approved as a replacement for lockwire?
Only where your drawing, process spec or maintenance data allows it. SAE AS4536 is the procurement specification and requirements for use for safety cable kits, and SAE AS567L covers safety cable alongside safety wire for propulsion systems. If the drawing calls NASM33540 lockwire only, changing to cable is an engineering decision, and installers need the matched tool and training.
How do I read a Dzus stud marking?
The FAA General handbook gives the example F 6 1/2 0.50. F is the flush head style, 6 1/2 is the body diameter in sixteenths of an inch, and 0.50 is the stud length in inches, measured from the head to the bottom of the spring hole. Match the length to the panel stack-up.
Do quarter-turn panel fasteners need a qualified source?
Under MIL-F-5591C, nonstructural panel fasteners had to be qualified for listing on the applicable qualified products list. That document is now superseded by NASM5591, so check what the current revision and your drawing require. If the drawing calls a manufacturer's part number, buy that exact part from the manufacturer or its authorized distribution.
Can safety wire be reused?
No. AC 43.13-1B says to cut safety wire close to the hole when removing it and never twist it off with pliers, and new wire is installed every time. Wire that is nicked, kinked or overtwisted is weakened and can break under vibration. Buy enough wire for rework and reinspection, not only for first assembly.
Related
Sources
- FAA-H-8083-30A Aviation Maintenance Technician Handbook, General, Chapter 7 captive fasteners and safetying
- FAA AC 43.13-1B, Chapter 7 Section 7, safetying
- EverySpec, MIL-F-5591C Fasteners, Panel, Nonstructural, superseded by NASM5591
- EverySpec, MIL-F-25173A Notice 2, reactivation
- EverySpec, MS20995E Wire, Safety or Lock, superseded by NASM20995
- EverySpec, MS33540J Safety Wiring and Cotter Pinning, superseded by NASM33540
- SAE Mobilus, AS567L safety cable, safety wire, key washers and cotter pins
- SAE Mobilus, AS4536 safety cable kit procurement specification
- Aircraft Spruce, MS20995 stainless safety wire
- Daniels Manufacturing, Safe-T-Cable product information
- SAE AS6174, Counterfeit Materiel
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