Cleco fasteners for sheet metal alignment and temporary assembly
What cleco fasteners are used for
Cleco fasteners are reusable temporary fasteners used to hold sheet metal, panels, brackets, skins, and small fabricated parts in position before permanent riveting, bolting, bonding, or welding. They are especially common in aircraft sheet metal repair, race car bodywork, prototype fabrication, HVAC work, and general metal layout. Their main value is alignment: a cleco passes through matched holes and clamps the stacked materials so the holes do not shift while the rest of the assembly is drilled, deburred, fitted, or riveted.
In workshop use, “cleco” is often used broadly for spring-loaded temporary sheet-metal holders, even when the part is sold under another temporary-fastener brand. For related fastening topics, see the Fasteners section.
How a cleco fastener works
A standard plier-operated cleco has a cylindrical body, a spring-loaded plunger, a pair of jaws or step-cut locks, and a spreader bar. When the plunger is compressed with cleco pliers, the jaws extend and narrow so they can pass through a drilled hole. When the pliers are released, the spring retracts the mechanism, the jaws expand on the far side of the material, and the fastener pulls the stacked sheets together.
The Federal Aviation Administration’s Aviation Maintenance Technician Handbook—Airframe describes cleco fasteners as reusable sheet-metal holders that keep separate sheets aligned when correctly installed. That point matters because a cleco is not a structural fastener. It is a temporary holding device used during a controlled assembly process, not a substitute for the specified permanent fastener or joint.
Because most standard clecos are blind temporary fasteners, the installer usually does not need access to the back side of the workpiece. This makes them useful on curved skins, closed panels, and assemblies where ordinary clamps cannot reach. The hole still has to match the chosen fastener. A loose cleco can allow movement; an undersized or burred hole can scratch material, damage a coating, or make removal difficult.
Main types of cleco fasteners
Plier-operated spring clecos
The standard spring cleco is the familiar fastener used with cleco pliers. It is quick to install, quick to remove, and well suited to repeated trial fitting. Manufacturer catalog data commonly lists standard plier-operated series with a grip range up to 1/4 inch, while heavy-duty versions are often listed with a grip range up to 1/2 inch. The exact range depends on the series, so the catalog value should be checked before purchase.
These are the usual choice for thin sheet metal alignment where speed is more important than high clamp force. They are commonly placed in alternating holes while the remaining holes are drilled, reamed, countersunk, or riveted.
Wing nut and hex nut clecos
Wing nut and hex nut temporary fasteners are used when higher clamp-up pressure is needed than a basic spring cleco can provide. The FAA airframe handbook notes that these styles are used for temporarily fastening sheets when higher clamp-up pressure is required, with hex nut versions suited to quick installation and removal using the proper driver. Wing nut types can be tightened by hand, while hex nut types are better for production or repetitive work where a tool is available.
These styles are useful when the work stack is thicker, stiffer, or more likely to separate during drilling and fitting. They are slower than plier-operated clecos, but they provide more controlled clamping.
Side-grip and edge clamps
Side-grip cleco clamps work differently because they can hold material near an edge without passing through a pre-drilled fastener hole. They are useful during bonding, sealant work, edge alignment, and operations where no hole should be introduced yet. Catalog listings commonly describe side-grip clamps by clamp capacity and reach rather than by drill size.
The limitation is access. A side-grip clamp works only where its jaws can reach the edge or flange. For internal holes across a wide panel, standard clecos are usually the more practical option.
Common sizes, color codes, and drill references
Cleco sizing is usually tied to hole diameter. The FAA handbook describes common cleco diameters including 3/32, 1/8, 5/32, 3/16, 1/4, and 3/8 inch. Manufacturer catalog tables also use color coding for quick size recognition. Color systems can vary by manufacturer and series, but the table below reflects a common catalog pattern for many plier-operated temporary sheet-metal fasteners.
| Nominal cleco diameter | Common color code | Typical drill reference | Common use note |
|---|---|---|---|
| 3/32 inch | Zinc or silver | #40 | Small holes, light sheet work, close layout work |
| 1/8 inch | Copper | #30 | Very common for general sheet metal and aircraft-style layout |
| 5/32 inch | Black | #21 | Medium fastener-hole work where larger rivets or screws are planned |
| 3/16 inch | Brass or gold tone | #10 | Heavier sheet or larger fastener locations |
| 1/4 inch | Copper in some catalog series | 1/4 inch | Larger temporary holding points and heavier assemblies |
| 3/8 inch | Varies by series | 3/8 inch or catalog-specified drill | Specialty use; always verify series data |
The drill reference is not a substitute for the engineering drawing, aircraft maintenance instruction, rivet specification, or fastener manufacturer’s data. It is only a selection aid. Final hole size, reaming, deburring, countersinking, and surface treatment should follow the procedure for the permanent fastener being installed.
How to choose the right cleco fastener
Start with the hole size. A cleco should fit the drilled hole snugly enough to prevent shifting, but not so tightly that it damages the hole or coating. If the hole will later be final-drilled or reamed, use the temporary fastening method specified for that sequence rather than guessing.
Next, check grip range. Grip range is the total material thickness the cleco can clamp. A standard plier-operated cleco may be suitable for thin sheets, but a thicker stack may need a heavy-duty, wing nut, long wing nut, hex nut, or long hex nut style. If the fastener is too short for the stack, it may not lock correctly. If it is far outside the intended grip range, clamp force and alignment can become unreliable.
Then consider the clamp force required by the job. For quick positioning, ordinary spring clecos are efficient. For stiff material, formed flanges, curved skins, or parts that tend to separate, wing nut or hex nut temporary fasteners provide stronger clamping. For edges where a hole is not available, side-grip clamps are the better choice.
Tooling also matters. Standard spring clecos require cleco pliers. Hex nut temporary fasteners may use a hex driver or pneumatic installer in production settings. Side-grip clamps usually use the same general style of temporary-fastener pliers, but buyers should verify compatibility because brands and series differ. See also: Buying Guides.
Installation and removal practices that protect the work
A good cleco setup starts with clean, accurately matched holes. Drill the pilot or fastener hole according to the work procedure, remove burrs when the process calls for it, and keep chips out from between the sheets. Chips trapped between layers can create false alignment and leave surface marks after clamping.
Use enough clecos to prevent movement, but do not assume more is always better. In many sheet-metal operations, clecos are placed in alternating holes so open holes remain available for drilling, reaming, deburring, countersinking, or riveting. As permanent fasteners are installed, clecos are removed in a controlled sequence so the joint does not relax or creep out of position.
Do not use a cleco as a pry point. If a panel does not fit, forcing it with temporary fasteners can enlarge holes, distort thin sheet, or hide a fit-up problem that will appear later during final fastening. The cleco should hold an aligned assembly, not correct a poorly fitted one.
Inspection is simple but important. Retire clecos with weak springs, bent jaws, damaged plungers, heavy corrosion, or inconsistent action. A worn fastener can feel installed while providing poor clamp force. For precision assemblies, keeping sizes sorted by color and diameter reduces mistakes and speeds up work.
Limits and common mistakes
The most common mistake is treating clecos as permanent fasteners. They are temporary holding tools, not load-bearing hardware. They should be removed and replaced by the specified rivet, screw, bolt, bonded joint, weld, or other permanent fastening method.
A second mistake is ignoring material compatibility and surface finish. Clecos are widely used on aluminum sheet, but they may also appear in work involving steel, stainless, plastic, or composite panels. Different materials can scratch, gall, chip, or crush in different ways. Protective caps, no-mar styles, controlled clamp force, or alternative fixturing may be needed where surface finish matters.
A third mistake is relying on color alone. Color is helpful, but the part marking, measured diameter, catalog series, and drill reference matter more. This is especially true when tools from different suppliers are mixed in one shop.
Finally, clecos do not replace a proper assembly plan. Hole sequence, fastener spacing, edge distance, deburring, countersinking, and final inspection still determine whether the finished joint is reliable. The cleco only helps hold the parts in the correct position while those steps are performed.
Frequently asked questions
Are cleco fasteners reusable?
Yes. Cleco fasteners are designed to be reused many times, provided the spring, jaws, plunger, and body remain in good condition. Damaged or weak fasteners should be replaced because poor clamping can allow parts to shift.
Are cleco fasteners permanent?
No. They are temporary alignment and clamping tools. Once the permanent rivets, screws, bolts, adhesive, welds, or other joining method is ready, the clecos are removed in the correct sequence.
What cleco size is used for a 1/8 inch hole?
A 1/8 inch cleco is commonly associated with a #30 drill reference in many catalog tables and is often color coded copper. Always confirm the required final hole size from the drawing, repair manual, or fastener specification.
Do side-grip clecos need drilled holes?
No. Side-grip cleco clamps are used at edges or flanges where their jaws can reach the work. They are helpful when a temporary hold is needed before drilling or where a hole is not desired.
How many clecos should be used on a panel?
There is no universal number. Use enough to prevent shifting while leaving access for the next operation. The right pattern depends on panel stiffness, hole spacing, curvature, material thickness, and the required assembly sequence.
