Last updated on August 31st, 2026 at 10:40 am
Standard steel self-clinching hardware is commonly used in aluminum and mild-steel sheet because it is widely available in many sizes and configurations. But choosing the right hardware for a custom sheet metal part involves more than simply matching the fastener material to the sheet material.
The correct hardware depends on the sheet material, material hardness, sheet thickness, mounting-hole requirements, fastener family, finishing process, corrosion environment, and electrical requirements.
One of the most important rules: don't specify self-clinching hardware by material alone. A stainless steel fastener, for example, is not automatically suitable for installation in stainless steel sheet.
Why Sheet Material and Hardness Matter
Self-clinching hardware works by being pressed into a properly sized hole in the sheet. During installation, panel material flows into features in the fastener, mechanically locking it into the sheet.
For that process to work correctly, the sheet must meet the hardware manufacturer's requirements for:
- Material hardness
- Sheet thickness
- Mounting-hole size
- Edge distance
- Installation force
- Fastener style and shank length
In general, the self-clinching fastener must be sufficiently harder than the sheet material for proper installation.
This is why choosing hardware based only on whether it is “steel” or “stainless steel” can cause problems.
Choosing Hardware for Aluminum and Mild Steel
Aluminum and mild steel are commonly used with a wide range of self-clinching hardware.
Depending on the specific fastener family and application, options may include steel, stainless steel, or aluminum hardware.
The best choice depends on more than the sheet material. Engineers should also consider:
- Required mechanical performance
- Panel hardness
- Sheet thickness
- Corrosion exposure
- Weight requirements
- Finishing process
- Electrical conductivity or grounding requirements
Standard steel hardware can be an economical option for many aluminum and mild-steel parts, but it should not automatically be selected when the finishing process or service environment creates additional requirements.
Choosing Hardware for Stainless Steel Sheet
Stainless steel sheet requires additional attention because the panel itself can be significantly harder than aluminum or mild steel.
Standard stainless steel self-clinching hardware is not automatically suitable for installation in stainless steel sheet.
Different self-clinching fastener families have different hardness limits. Hardware designed for aluminum and mild steel may not clinch properly into harder stainless sheet, even when the fastener itself is made from stainless steel.
If the fastener is not sufficiently hard relative to the panel, the sheet material may not flow correctly into the fastener's locking features. This can result in poor retention, spinning hardware, or hardware that pushes out under load.
For stainless steel sheet, use a self-clinching fastener family specifically rated by the manufacturer for the hardness of the stainless material being used.
Don't Forget Sheet Thickness and Shank Length
Material compatibility is only part of hardware selection.
Self-clinching fasteners also have minimum sheet-thickness requirements, and many fastener families are available with different shank lengths for different panel thicknesses.
When specifying hardware, verify:
- Exact manufacturer part number
- Thread size
- Shank code or length
- Minimum sheet thickness
- Maximum panel hardness
- Required mounting-hole diameter
- Minimum edge distance
Using the correct mounting hole is particularly important. A hole that is oversized, undersized, or incorrectly manufactured can prevent the fastener from developing the intended retention strength.
For more on this subject, see our guide to accurate hardware hole sizes for self-clinching fasteners.
Hardware Material Selection Guide
| Sheet or Application | Hardware Consideration |
|---|---|
| Aluminum Sheet | Many steel, stainless steel, and aluminum self-clinching families may be available. Verify the specific fastener's panel hardness and thickness requirements. |
| Mild Steel Sheet | Standard self-clinching hardware is commonly available. Verify sheet hardness, thickness, hole size, and finishing requirements. |
| Stainless Steel Sheet | Use hardware specifically rated for the hardness of the stainless sheet. Standard stainless hardware may not be suitable. |
| Corrosive Environment | Consider hardware material, sheet material, galvanic compatibility, protective finish, and environmental exposure together. |
| Anodized Aluminum | Determine the hardware installation sequence and masking requirements before production. |
| Powder-Coated Parts | Consider coating buildup, threads, electrical contact surfaces, masking, and hardware installation sequence. |
Here's our downloadable hardware reference sheet for additional guidance:
Coating and Surface Treatment Implications
Hardware selection also needs to account for what happens to the part after fabrication. Powder coating, anodizing, chromate conversion coating, plating, and other finishing processes can affect hardware installation sequence, corrosion resistance, electrical contact, threads, and final assembly fit.
There is no universal rule that hardware should always be installed before or after finishing. The correct sequence depends on the sheet material, hardware, finish specification, and functional requirements of the assembly.
Powder Coating
Self-clinching hardware can be installed before powder coating in many applications, but the effect of the coating on the hardware needs to be considered.
If powder coating is applied after hardware insertion, identify any surfaces that need to remain free of coating.
Common masking considerations include:
- Internal and external threads
- Grounding and bonding surfaces
- Electrical contact points
- Critical mating surfaces
- Hardware features where coating buildup could interfere with assembly
Powder coating also requires an elevated-temperature cure cycle, so temperature-sensitive inserts, plastics, adhesives, seals, or other components may need to be installed after finishing.
Anodizing
Anodizing is primarily used on aluminum. Steel and stainless steel hardware do not become anodized simply because they are installed in an aluminum part.
If an aluminum sheet metal part requires anodizing, determine the hardware installation sequence before manufacturing begins.
Do not assume that steel, stainless steel, or aluminum hardware can automatically remain installed through the anodizing process. The appropriate sequence depends on the hardware, anodizing specification, electrical contact requirements, masking requirements, and desired appearance.
If hardware must be installed before anodizing, confirm compatibility with both the hardware manufacturer and the finishing requirements.
Chromate Conversion Coating, Plating, and Other Chemical Finishes
Chemical finishing processes should also be evaluated individually rather than applying a single rule based on the hardware material.
Different finishing processes use different chemistries and process conditions. Installed hardware can affect how the part reacts during processing, while the process itself can affect the hardware's finish, corrosion protection, appearance, or function.
If hardware will be present during chromate conversion coating, plating, passivation, or another chemical treatment, confirm that the specific hardware and process are compatible.
Consider Galvanic Corrosion Between the Hardware and Sheet
Hardware material can also affect corrosion resistance after the assembly enters service.
When dissimilar metals are electrically connected and exposed to moisture or another electrolyte, galvanic corrosion can occur.
For example, stainless steel hardware installed in aluminum sheet may require additional consideration in an outdoor, marine, high-humidity, or otherwise corrosive environment.
The actual corrosion risk depends on factors including:
- Hardware and sheet materials
- Service environment
- Moisture and chemical exposure
- Relative exposed surface areas
- Coating and pretreatment systems
- Assembly geometry
- Required service life
Do not select hardware material based solely on corrosion resistance of the fastener itself. Consider the complete material combination and service environment.
Account for Coating Thickness and Final Fit
Powder coating, paint, plating, and other finishes can add measurable thickness to coated surfaces.
This can affect hardware and assembly features such as:
- Threads
- Close-fitting holes and slots
- Mating surfaces
- Electrical contacts
- Sliding interfaces
- Hardware clearances
Rather than planning to re-tap coated threads afterward, identify threads and other functional surfaces that need to remain free of coating so they can be properly masked or otherwise protected during finishing.
Specify the Exact Hardware Part Number
A drawing callout such as “stainless PEM nut” does not provide enough information to select hardware reliably.
Different self-clinching fastener families can have different:
- Materials
- Hardness levels
- Sheet-thickness requirements
- Mounting-hole sizes
- Shank lengths
- Installation forces
- Mechanical performance
Whenever possible, specify the exact manufacturer and part number on the fabrication drawing or bill of materials.
If alternate hardware is acceptable, identify that as well. An alternate manufacturer or fastener family should not automatically be treated as a drop-in replacement without verifying its installation and performance requirements.
Self-Clinching Hardware Selection Checklist
Before releasing a custom sheet metal design, verify:
- Sheet material: Aluminum, mild steel, stainless steel, or another material
- Sheet thickness: Confirm it meets the fastener's minimum requirements
- Panel hardness: Confirm the hardware is rated for the sheet material and condition
- Part number: Specify the exact manufacturer and fastener
- Shank length: Select the appropriate option for the sheet thickness
- Mounting hole: Use the manufacturer's specified hole size
- Edge distance: Maintain the required distance from nearby edges and features
- Finish: Determine whether hardware should be installed before or after finishing
- Masking: Identify threads, grounding points, mating surfaces, and other areas that must remain free of coating
- Corrosion: Consider galvanic compatibility and the service environment
- Performance: Verify pushout, torque-out, or other mechanical requirements when they are important to the application
What ASM Needs on Your RFQ
When your custom sheet metal part requires self-clinching hardware, provide the exact hardware callouts with the RFQ whenever possible.
Include:
- 3D CAD model
- Fully dimensioned 2D drawing
- Sheet material and thickness
- Hardware manufacturer and part number
- Hardware quantity and location
- Finish specification
- Masking requirements
- Grounding or electrical contact requirements
- Any critical hardware performance or inspection requirements
If your drawing only identifies a generic hardware type, Approved Sheet Metal can review the application during quoting, but clarification may be required before the correct fastener can be selected.
Choose Hardware as Part of the Complete Sheet Metal Design
The right hardware isn't simply a choice between steel, stainless steel, and aluminum. Successful self-clinching hardware installation depends on the relationship between the fastener, sheet material, material hardness, thickness, mounting hole, finish, and service environment.
Planning those requirements early helps prevent spinning hardware, poor retention, finishing problems, corrosion issues, and unnecessary design changes after parts have already entered production.
At Approved Sheet Metal, we can review hardware requirements as part of the complete fabrication process and help identify potential manufacturability issues before production.
Request a quote for your next custom sheet metal fabrication project.
Sheet Metal Hardware Hole Sizes Chart
CHART DOWNLOAD
Hardware hole sizes are the number one thing sheet metal fabricators have to fix before sending a part to the floor. So we have created a referenceable chart for product developers that are designing sheet metal parts. Use this chart to find the correct hole size for the hardware you select.
