How cleco fasteners improve sheet metal alignment before riveting
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What cleco fasteners do in sheet metal work
Cleco fasteners are reusable temporary fasteners used to hold drilled sheet metal, panels, brackets, skins, and small fabricated parts in alignment before permanent fastening. Their job is straightforward but critical: they keep matched holes from shifting while a technician drills, deburrs, test-fits, bonds, welds, or rivets an assembly. In aircraft maintenance, race car fabrication, prototype work, HVAC sheet metal, and general metal layout, that temporary holding force can reduce rework and help parts stay in the intended position until the final fastener is installed.
A cleco is not a permanent structural fastener. It is a workholding device. Once the assembly is ready for a rivet, screw, bolt, weld, or bond line, the cleco is removed from that location and replaced by the specified final fastening method. In regulated work such as aircraft repair, the approved maintenance data, drawing, or engineering instruction should always control the final hole size, fastener type, edge distance, spacing, and inspection steps.
For broader fastening terminology and related hardware topics, see the Fasteners section.
How a standard spring cleco works
The familiar plier-operated cleco has a cylindrical body, a spring-loaded plunger, two step-cut locking jaws, and a spreader bar. When cleco pliers compress the plunger, the jaws extend and narrow so they can pass through a drilled hole. When the pliers are released, the spring retracts the jaws against the spreader bar. The jaws spread behind the lower sheet, pulling the stack toward the cleco body and clamping the material between the body and the jaw steps.
This blind clamping action is one reason clecos are useful in sheet metal assembly. The worker does not always need hand access to the back side of the panel to start alignment. A row of clecos can hold a skin, doubler, bracket, or panel in position while additional holes are match-drilled or while permanent fasteners are installed one at a time.
In practice, clecos are usually installed after pilot or final-size holes are drilled through the mating parts. A typical workflow is to drill and secure one hole, align the part, drill the next hole, add another cleco, and continue across the joint. The spacing pattern depends on panel stiffness, curvature, hole tolerance, and the procedure being followed. Thin flat sheet may need fewer temporary fasteners than a curved aircraft skin or a springy repair doubler.
Common cleco types and where each one fits
Although many people use the word cleco for nearly all temporary sheet-metal holders, the term covers several useful styles. The right choice depends on required access, clamp force, material thickness, surface sensitivity, and installation speed.
Spring clecos
Spring clecos are the most common style in light sheet metal work. They are quick to install with hand pliers, reusable, compact, and suitable for holding parts in alignment during drilling and riveting. They are especially practical when many holes must be opened and closed repeatedly during layout. Their main limitation is clamp force: they hold parts together, but they may not pull distorted, curved, or highly stressed parts into close contact if the stack wants to spring apart.
Wing nut and hex nut clecos
Wing nut and hex nut temporary fasteners are used when more clamping force is needed than a standard spring cleco can provide. Instead of relying only on spring action, these styles tighten mechanically. Wing nut versions can be adjusted by hand; hex nut versions are often used where tighter spacing or tool-driven installation is preferred. Manufacturer literature commonly warns that torque-controlled tools help prevent damage when threaded temporary fasteners are tightened, because excessive torque can mark the work, distort a hole, or overload thin material.
Cylindrical and power-installed temporary fasteners
Cylindrical body temporary fasteners are common in higher-volume or production-style environments where repeatability and installation speed matter. They may use dedicated manual or pneumatic tools. The benefit is consistent installation in repetitive assemblies, but the tradeoff is more specialized tooling and closer attention to the fastener series, grip range, and driver setup.
Side-grip and edge clamps
Side-grip clamps are related temporary workholding tools used at panel edges or in locations where there is no drilled through-hole for a standard cleco. They can hold edges during bonding, sealing, fitting, and layout. They do not replace through-hole clecos when hole alignment is the main requirement, but they are useful companions when a panel needs both edge control and hole-to-hole alignment.
Choosing diameter, drill size, and grip range
Cleco selection starts with the hole, not the color. The cleco diameter must match the intended hole size closely enough to align the sheets without forcing the hole or allowing excessive movement. The grip range must also match the total stack thickness, including skins, doublers, shims, brackets, and any temporary material used during fitting.
Color coding helps technicians identify sizes quickly, but it should be treated as a common shop convention rather than a universal substitute for measuring. Supplier catalogs and job instructions may vary, especially for specialty temporary fasteners. Always confirm the fastener diameter, grip range, and drill reference before using clecos on precision or regulated work.
| Common cleco diameter | Common color code | Typical drill reference | General use note |
|---|---|---|---|
| 3/32 inch | Silver or zinc | #40 | Small rivet holes, thin sheet, close layout work |
| 1/8 inch | Copper | #30 | Common light sheet metal and aircraft-style repair layouts |
| 5/32 inch | Black | #20 | Larger rivet locations or heavier sheet assemblies |
| 3/16 inch | Brass or gold tone | #10 | Heavier panels, brackets, and larger fastener holes |
| 1/4 inch | Often green or copper depending on series | 1/4 inch | Specialty or heavier temporary holding applications |
Grip range is just as important as diameter. A cleco that is too short may not lock correctly behind the stack. A cleco that is too long may feel loose or fail to produce the intended clamping action. Standard spring clecos are often associated with relatively thin stack-ups, while wing nut, hex nut, heavy-duty, long-grip, and extended-grip styles cover thicker or more demanding assemblies. The exact range is product-specific, so supplier data should be checked when the stack thickness is near the limit.
Where clecos add the most value
The strongest use case for clecos is not simply holding two pieces together. Their real value is controlled sequencing. They let a fabricator build an assembly gradually, check fit as work progresses, and keep previously drilled holes from wandering while new holes are added. See also: Buying Guides.
- Aircraft sheet metal repair: Clecos help hold skins, ribs, stiffeners, doublers, and patches during drilling and riveting. The final repair still depends on approved data and inspection requirements.
- Motorsport and race car fabrication: Panels, floor sections, aluminum bodywork, and brackets can be test-fitted repeatedly before rivets or quarter-turn hardware are installed.
- Prototype and low-volume fabrication: Clecos make it easier to assemble and disassemble parts during design checks before committing to permanent fasteners.
- HVAC and duct work: Temporary alignment can help with repeatable hole placement and trial fitting before screws, rivets, or seams are completed.
- Composite and honeycomb-related setups: Specialty non-marking or knurled temporary fasteners may be selected where surface protection and controlled grip are more important than basic metal-to-metal clamping.
Clecos are especially useful when a job involves several rounds of checking. If a panel must be removed for deburring, cleaning, sealant application, or inspection, a known cleco pattern helps the part return to the same hole alignment before final fastening.
Installation sequence that reduces misalignment
A good cleco setup is methodical. Rushing the sequence can trap stress in the panel, enlarge holes, or create a small alignment error that becomes obvious only after final riveting.
- Prepare and mark the parts. Confirm the drawing, template, or layout marks before drilling. Check that edges, bends, and reference points are correctly oriented.
- Clamp the first reference area. Use clamps, tape, fixtures, or edge tools as needed so the first hole is drilled in the intended location.
- Drill the first hole and install a cleco. The first cleco becomes a pivot point, so place it where it supports the alignment strategy.
- Align the opposite end or a second reference hole. This prevents the part from rotating around the first cleco.
- Work outward in a controlled pattern. Add holes and clecos progressively rather than drilling an entire row without temporary holding.
- Remove parts for deburring when required. Burrs can hold sheets apart and create false clamp pressure.
- Reassemble and replace clecos with final fasteners in sequence. Remove only the cleco needed for the next rivet or fastener unless the procedure calls for a different pattern.
This sequence is not a substitute for a formal work instruction. It reflects the main principle behind temporary fastening: preserve alignment while still allowing inspection, cleaning, and staged assembly.
Common mistakes and practical limits
Most cleco problems come from using the right-looking fastener in the wrong hole, the wrong grip range, or the wrong material condition. A cleco should slide into the hole when compressed; it should not be hammered, twisted aggressively, or used to correct a badly misplaced hole. Forcing a cleco can elongate the hole, mark the surface, or hide an alignment problem that should be fixed before final assembly.
- Using color alone: Color is helpful, but diameter and drill reference should be confirmed for the fastener series in use.
- Ignoring grip range: Too little or too much stack thickness can reduce clamping reliability.
- Skipping deburring: Burrs between sheets can prevent full contact and lead to poor final fit.
- Over-tightening threaded styles: Wing nut and hex nut fasteners can apply much more force than spring clecos, so excessive torque can damage workpieces.
- Leaving clecos in final assemblies: Clecos are temporary. They must be removed and replaced by the specified permanent fastening method.
- Using damaged clecos: Bent jaws, weak springs, worn plungers, and contaminated threads reduce holding performance and can damage holes.
Surface-sensitive materials deserve special attention. Painted, polished, composite, or soft aluminum surfaces may need non-marking accessories, protective tape, clean tools, or alternative temporary fasteners. Where sealant or adhesive is involved, the sequence should also account for squeeze-out, cleanup, cure time, and the risk of bonding a temporary fastener into place.
Frequently asked questions
Are cleco fasteners the same as rivets?
No. A cleco is a reusable temporary fastener used during fitting, drilling, and assembly. A rivet is a permanent fastener. Clecos hold the parts in position until the rivets or other final fasteners are installed.
Can clecos be used without special pliers?
Standard spring clecos are designed for cleco pliers or the correct installation tool. Threaded wing nut or hex nut versions use a different tightening method. Using improvised tools can damage the cleco, the hole, or the work surface.
How many clecos are needed for a panel?
There is no single number. It depends on panel size, stiffness, curvature, hole spacing, and the accuracy required. A flexible or curved panel usually needs more temporary fasteners than a small flat bracket. The goal is to prevent hole shift and sheet separation while still allowing access for drilling, deburring, and final fastening.
Do cleco color codes always mean the same thing?
Common shop color codes are widely used, such as copper for 1/8 inch and black for 5/32 inch, but color should not be the only reference. Specialty lines and suppliers may differ, so confirm the marked size or product data before precision work.
Can clecos damage sheet metal?
They can if they are forced into the wrong hole, used with the wrong grip range, over-tightened, or installed with damaged jaws. Correct size selection, clean holes, deburring, and appropriate surface protection reduce the risk.
Bottom line
Cleco fasteners are simple tools with a significant effect on sheet metal accuracy. By temporarily clamping matched holes, they help fabricators control fit, sequence, and repeatability before permanent fastening. The best results come from matching diameter and grip range to the job, choosing the right style for the required clamping force, and treating clecos as precision workholding devices rather than rough clamps. Used correctly, they make drilling, fitting, and riveting more predictable without becoming part of the finished assembly.
