Find the Right Shank Code for Your Hardware (Updated for 2026)

Last updated on August 17th, 2026 at 08:24 am

Do you know which self-clinching PEM® nut has the correct shank code for your precision fabrication project?

The correct PEM® nut shank code depends on the fastener series, thread size, host material, material hardness, and sheet thickness. Shank codes such as 0, 1, 2, and 3 identify different shank lengths within a particular PEM® fastener family, so the right code should be selected from the manufacturer's dimensional data for the exact fastener being used.

In most of the sheet metal forming world, and here at Approved Sheet Metal, PEM® hardware is a common choice for self-clinching nuts. A common alternative to welding a separate nut in place, self-clinching nuts provide permanent load-bearing threads in sheet metal that may be too thin to tap directly.

When self-clinching nuts are inserted and pressed into a properly sized mounting hole, installation pressure causes the surrounding sheet material to cold-flow into an undercut in the fastener. The clinching feature then mechanically locks the nut into the sheet and helps resist rotation.

Why PEM® Shank Size Matters

Shank size plays an important role in how a self-clinching nut installs into the sheet, and engineers need to choose hardware that is compatible with the thickness of the host material.

Shank size must be matched to material thickness.

• If the selected shank is not appropriate for the sheet thickness, the fastener may not seat as intended or may protrude excessively from the opposite side of the material.
• If the sheet is below the minimum thickness specified for the fastener, there may not be enough material available to properly cold-flow into the undercut and develop the intended retention.
• If the hardware is changed after the material thickness changes, the shank code should be reviewed again rather than assuming the original fastener will still work.

The important point is that a shank code is not a universal sheet-thickness designation. Shank code 1, for example, does not automatically correspond to one specific material thickness across every PEM® product family and thread size.

What Determines the Correct PEM® Nut Shank Code?

To select the correct self-clinching nut, identify these factors:

• Fastener series: S, SS, CLS, CLSS, SP, CLA, or another applicable PEM® product family
• Thread size: Such as #4-40, #6-32, M3, M4, etc.
• Host material: Steel, stainless steel, aluminum, or another compatible sheet material
• Material hardness: The sheet must be softer than the fastener and within the manufacturer's specified hardness range
• Sheet thickness: The actual material thickness must meet the requirements for the selected shank code
• Mounting-hole diameter: The hole must match the dimensional requirement for the specific fastener

Once those factors are known, the PEM® dimensional table can be used to select the compatible shank code.

Sheet Thickness Isn't the Only Requirement: Check Material Hardness

Selecting a shank code that matches the sheet thickness does not automatically mean the fastener is appropriate for the material.

Different PEM® nut families are designed for different host-material hardness ranges. Current PEM® specifications include:

• S/SS nuts are recommended for use in steel or aluminum sheets HRB 80 / HB 150 or less.
• CLS or CLSS nuts are recommended for use in steel or aluminum sheets HRB 70 / HB 125 or less.
• SP nuts are recommended for use in stainless steel sheets HRB 90 / HB 192 or less.
• CLA nuts are recommended for use in steel or aluminum sheets HRB 50 / HB 82 or less.

That means two parts with the same material thickness may require different hardware depending on the material and hardness of the sheet.

How to Select the Shank Code for Your Precision Fabrication

We frequently help customers select hardware for their sheet metal forming projects at Approved Sheet Metal. But if you want to identify the appropriate shank code before submitting a design, we’ve created a handy guide to simplify the process.

Here's how to use this sheet metal hardware chart:

1. Identify the host material and hardware type.

Start with the sheet material, then locate the appropriate style of self-clinching PEM® nut. The hardware series must be compatible with the hardness of the material receiving the fastener.

2. Choose the corresponding thread code.

Select the required thread size for the mating hardware. We've provided both standard and metric thread codes for convenience.

3. Find the applicable sheet thickness.

Use the actual sheet thickness specified for the part rather than selecting hardware from thread size alone.

4. Identify the corresponding shank code.

Use the hardware type, thread size, and material thickness together to determine which shank code is appropriate.

5. Verify the specified mounting-hole diameter.

The mounting hole is part of the self-clinching system. Use the hole size specified for the exact PEM® fastener rather than treating it like an ordinary screw clearance hole.

6. Confirm material hardness and performance requirements.

Before finalizing the hardware, verify that the host material meets the hardness requirements and review any required push-out, torque-out, finish, or application-specific performance.

For example, using the specific M3 hardware represented in our chart, 0.040" material corresponds to shank code 1, while 0.074" material corresponds to shank code 2.

Those examples should not be treated as a universal rule for every M3 self-clinching nut. Always verify the fastener family and manufacturer's data for the exact part number being specified.

Don't Treat the PEM® Mounting Hole Like a Normal Clearance Hole

The mounting-hole diameter is critical to proper self-clinching hardware installation.

PEM® fasteners are designed to be installed into a specified punched or drilled hole. During installation, material surrounding that hole must move into the fastener's undercut to create the mechanical lock.

If the hole is too large, too small, or otherwise outside the specified range, the fastener may not develop the expected seating, torque-out, or push-out performance.

Engineers generally should not resize the mounting hole based solely on normal screw-clearance practices. Use the mounting-hole dimension specified for the exact self-clinching fastener.

How to Use Shank Codes to Choose the Right PEM® Nuts

Once you know which shank code you need, you can identify the complete PEM® part number for your custom sheet metal part.

PEM® part numbers communicate information such as:

• Fastener family or style
• Thread size
• Shank code
• Fastener material
• Finish or other options, when applicable

The exact naming convention varies between PEM® product families, so it is better to verify the complete manufacturer's part number than to assume every designation follows exactly the same structure.

For example, the part number CLA-632-2 identifies a CLA-series self-clinching nut with:

• Thread code: 632
• Shank code: 2
• PEM® product family: CLA

Let's look at another example. The part number CLS-440-1 identifies a CLS-series nut with:

• Thread code: 440
• Shank code: 1
• PEM® product family: CLS

Using the complete part number on the drawing helps remove ambiguity and ensures that the fabricator knows exactly which hardware the design requires.

How to Read a PEM® Spec Sheet for Shank Code Selection

When selecting a self-clinching PEM® nut for a sheet metal project, the manufacturer's spec sheet provides the information needed to verify whether the hardware is appropriate for the part.

1. Identify the Hardware Type

PEM® self-clinching nuts come in various styles, each designed for particular materials, hardness ranges, thread sizes, and applications. Start by verifying the product family that is appropriate for the sheet material.

2. Locate the Minimum Sheet Thickness Requirement

Every self-clinching nut has an applicable sheet-thickness requirement. If the sheet is below the manufacturer's specified minimum, there may not be enough material to properly engage the clinching feature.

3. Find the Recommended Hole Size

PEM® nuts require a specified mounting-hole diameter for proper installation. The hole dimension varies with fastener type and thread size and should be taken directly from the manufacturer's dimensional data.

4. Determine the Correct Shank Code

The shank code identifies the applicable shank length within the selected fastener series. Use the dimensional table to correlate the selected hardware with the sheet thickness.

Do not select the shank code independently of the fastener series and thread size.

5. Review Torque-Out and Push-Out Resistance

PEM® performance data may include torque-out resistance and push-out force. These values can help engineers determine whether the selected fastener provides appropriate retention for the application.

6. Check Finish, Material, and Other Options

Depending on the product family, options can include:

• Different fastener materials
• Standard or metric threads
• Finish options, including those identified in PEM® finish specifications
• Special hardware styles such as floating, flush-mount, locking, or other application-specific fasteners

Common PEM® Hardware Selection Mistakes

Several common design mistakes can create hardware-insertion problems even when the correct thread size has been selected:

• Selecting hardware by thread size without checking sheet thickness
• Assuming one shank code represents the same thickness across every PEM® product family
• Ignoring host-material hardness requirements
• Using an incorrect mounting-hole diameter
• Changing sheet thickness without reevaluating the hardware part number
• Specifying hardware before the final material and thickness are established
• Failing to consider required torque-out, push-out, finish, or other application requirements

The key takeaway is simple: don't select a self-clinching PEM® nut from thread size alone. The correct hardware depends on the fastener family, thread size, host material, material hardness, sheet thickness, mounting-hole size, and application requirements.

If you already know the exact PEM® part number, include it on the drawing. If you aren't sure which hardware is appropriate, our team can review your material thickness and application and help identify the appropriate hardware before fabrication begins.

Request a quote to get started with Approved Sheet Metal today.