What Are Dzus Fasteners?
A quick guide to styles, sizes, and how to match studs, springs, and grommets.
Dzus fasteners are quarter-turn, self-locking panel fasteners made from heat-treated, cadmium plated nickel steel, used together with aluminum grommets and music wire springs. The system gives a secure, repeatable clamp that can be locked or released with a simple quarter turn, which makes it ideal for covers, plates, cowlings, and other panels that need quick removal and replacement on aircraft and vehicles.
When a stud is worn, bent, or broken, it must be replaced to maintain proper clamp and vibration resistance. Light-duty installations usually only require swapping the stud itself, while heavy-duty styles often require replacing the retaining grommet as well so the panel continues to locate and support correctly.
Who Invented Dzus Fasteners
The Dzus quarter-turn fastener was invented by William Dzus in the 1930s, originally for aircraft applications where quick access and secure retention were both critical. As aviation technology spread, these fasteners were adopted in heavy machinery, race cars, motorsports bodywork, and a wide range of custom and restoration projects where panels are removed frequently.
How Dzus Fasteners Are Identified
Each Dzus stud is identified by a type code (head style), a size number (body diameter), and a length code, plus optional letters that describe special features. Once you know how to read these three pieces, any part number on a drawing, IPC, or catalog page tells you exactly what to order.
Head Style Codes
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Type A - Oval Head Standard oval head with normal undercut. The general-purpose style, installed with or without a grommet.
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Type AJ - Oval Head, Long Undercut Same oval head as Type A, but the longer undercut lets the stud eject and sit proud of the panel when unlocked, so it is easy to grip by hand.
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Type F - Flush Head Sits flush with the panel surface. Used on cowlings and exterior panels where the fastener must not disturb airflow.
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Type FJ - Flush Head, Long Undercut Flush-head equivalent of AJ. The long undercut lets the stud eject for easy removal by hand.
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Type FA - Flush Head, Rounded Edge Heavier-duty flush style with a higher tensile rating. Made only in sizes 5 and 6-1/2.
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Type HF - Hex Head Hexagonal head for wrench operation instead of a screwdriver or Dzus key. Made only in size 7, on special order.
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Modifier Letters
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J - Long Undercut Stud ejects and recedes from the panel when unlocked, for easier hand access. Used on AJ and FJ.
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O - No Undercut Stud lifts completely free of the panel when unlocked. Special order only.
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W - Wing Added A wing is added to the head for tool-less hand turning. Can be added to A, AJ, F, FJ, or FA (for example FAW5-35 is the winged version of FA5-35).
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Matching Sizes to Styles
The number right after the head-style letters is the size family, and it tells you the stud's body diameter directly in sixteenths of an inch (a "5" is 5/16 inch, a "6-1/2" is 13/32 inch, and so on). Not every head style is made in every size. Use this table to see which combinations actually exist before you spec or quote a part.
| Size Code | Body Diameter | Approx. Tensile Strength | A / AJ Oval | F / FJ Flush | FA Heavy Duty | HF Hex |
| 3 | 3/16" | 350 lbs | Yes | Yes | - | - |
| 4 | 1/4" | 700 lbs | Yes | Yes | - | - |
| 5 | 5/16" | 1,000 lbs | Yes | Yes | Yes | - |
| 6 | 3/8" | 1,250 lbs | Yes | Yes | - | - |
| 6-1/2 | 13/32" | 1,500 lbs | Yes | Yes | Yes | - |
| 7 | 7/16" | 1,800 lbs | Yes | Yes | - | Yes* |
*HF7 is made only in three lengths (.400", .450", .500") of SAE X1314 steel, on special order.
Reading a Full Part Number
The number after the dash is the length code, read directly as a decimal in inches. Take FJ4-35: FJ is the head style, 4 is the size family, and 35 means a .350 inch working length.
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FJ Head Style
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4 Size / Diameter
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-35 Length (.350")
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A3-20 Oval head, 3/16" diameter, .200" length
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FJ4-35 Flush head, long undercut, 1/4" diameter, .350" length
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FAW5-35 Flush rounded-edge head with wing, 5/16" diameter, .350" length
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AO6-1/2-50 Oval head, no undercut, 13/32" diameter, .500" length
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Matching Springs and Grommets to the Stud
Once you know the stud family and size, the spring and grommet follow the same size number automatically. Springs and grommets also come in multiple heights within each size to fit different panel and support thickness stack-ups, so always confirm the height code against your actual stack, not just the size number.
| Stud Family | Spring Prefix | Grommet Prefix | Example |
| A / AJ (sizes 3 to 7) | S[size] | GA[size] | AJ5-45 pairs with S5 spring and GA5 grommet |
| F / FJ (sizes 3 to 7) | S[size] | GF[size] | FJ6-40 pairs with S6 spring and GF6 grommet |
| FA (sizes 5, 6-1/2) | S[size] | GF[size] | FA6-1/2-45 pairs with S6-1/2 spring and GF6-1/2 grommet |
| HF7 (size 7 only) | SH7 | Installed direct to panel, no grommet | HF7-45 pairs with SH7 spring, drilled into a surface plate |
Common Combinations in Vintage and Restoration Work
- Type A or AJ oval-head studs with GA grommets and S springs in light skins and access doors.
- Type F or FJ flush-head studs with GF grommets for cowlings and exterior panels that must stay flush with the airflow.
- Heavy-duty FA and HF styles in larger diameters where higher clamp loads or wrench operation are required.
Modern catalogs and suppliers also offer winged versions, captive grommet units, and special corner or side-mount springs that extend the original Dzus system into more complex panel geometries.
Dzus Hardware Visual Reference
The images below show the typical Dzus hardware types. For full engineering tables, tolerances, and special or on-order configurations, see the DZUS Quarter-Turn Self-Locking Fasteners Catalogue D-2 (1944).
