Self-clinching fasteners are a crucial part of custom sheet-metal enclosures and parts. They solve many challenges for mounting components. Plus, self-clinching fasteners provide high push-out and torque-out resistance, as well as strong threads in very thin material. Since self-clinching fasteners have fewer parts, you do not require extra hardware such as washers and loose nuts for final assembly. This gives you a streamlined design with less overall assembly time (and, by extension, low installation costs).

You’ve probably heard of these fasteners being referred to as their abbreviation PEM – that comes from Penn Engineering & Manufacturing Corp., which is the world’s leading manufacturer of self-clinching fasteners.

If you’ve ever looked at a part number for a self-clinching fastener, you likely have noticed the series of letters and numbers within the part number. This blog post will go through each portion of the part number, and decipher the codes that are associated with the self-clinching fasteners so that you can quickly decide on the best fastener for your specific needs.

Pictured above is a diagram of how each self-clinching fasteners name is broken down. Starting off in the left box is the style of fastener & material, in the middle is the thread code, followed by the length.

Styles of Fastener & Material

Our most popular self-clinching fasteners are nuts, studs and standoffs.

Nuts

There are six different codes associated with nuts: Carbon Steel Nut (S -) & (SS -), 300 Series Stainless Steel Nut (CLS -), 400 Series Stainless Steel Nut (SP -), Aluminum Nut (CLA -), Flush Nut (F -).

So, for example when figuring out the code for the self-clinching fastener, if you were using an Aluminum Nut, the first part of your code would be CLA.

Code in Fastener NameMeaning
S-Carbon Steel Nut
SS-Carbon Steel Nut
CLS-300 Series Stainless Steel Nut
SP-400 Series Stainless Steel Nut
CLA-Aluminum Nut
F-Flush Nut

Studs

There are three different codes for studs. They include Carbon Steel and Flush Head Stud (FH -), 300 Series Stainless and Flush Head Stud (FHS -), 400 Series Stainless and Flush Head Stud (FH4 -).

Code in Fastener NameMeaning
FH –Carbon Steel, Flush Head Stud
FHS – 300 Series Stainless, Flush Head Stud
FH4 – 400 Series Stainless, Flush Head Stud

Standoffs

Similar to nuts, self-clinching standoffs also have six different material codes: Carbon Steel and Thru-Hole Standoff (SO -), 300 Series Stainless and Thru-Hole Standoff (SOS -), 400 Series Stainless and Thru-Hole Standoff (SO4 -), Carbon Steel and Blind Standoff (BSO -), 300 Series Stainless and Blind Standoff (BSOS -), 400 Series Stainless and Blind Standoff (BSO4 -).

Code in Fastener NameMeaning
SO –Carbon Steel, Thru-Hole Standoff
SOS –300 Series Stainless, Thru-Hole Standoff
SO4 – 400 Series Stainless, Thru-Hole Standoff
BSO – Carbon Steel, Blind Standoff
BSOS – 300 Series Stainless, Blind Standoff
BSO4 –400 Series Stainless, Blind Standoff

Thread Code

Moving on, we have the second part of the code and that is the Thread Code. The Thread Code identifies the internal or external threads for the self-clinching fasteners. They will be either imperial or metric.

Usually, the code will be the same as the thread but just without the “-“. For example, a 4-40 threaded self-clinching fastener would be XXX-440-XXX).

The most common threads we use are:

  • 4-40
  • 6-32
  • 8-32
  • 10-32
  • 10-24
  • 1/4-20
  • M3
  • M4
  • M6

Length Code

Length code indicates the length of the standoff or stud, or it indicates the length of the shanks for self-clinching nuts.

TIP: Self-clinching fasteners with a Zinc finish will have “Zi” after the length code (XXX-XXX-1Zi).

Nuts

The length code for self-clinching nuts indicates the length of the shank. Typically, the longer the shank, the more force required to knock the fastener out of place. However, when the shanks length increases, the fastener’s minimum sheet thickness increases as well. Nuts have four different shank codes, as detailed below in the table.


Shank CodeMinimum Sheet Thickness
-00.030″
-10.040″
-20.056″
-30.090″

Studs

The length code for studs is measured in 1/16″ increments for imperial fasteners and millimeters for metric fasteners. The length of the stud is its actual length. Studs have three different length codes.

For imperial, with a fractional length of 4/16″ (1/4″) and a decimal inch length of 0.250″ the length code would be -4. For a fractional length of 6/16″ (3/8″) and a decimal inch length of 0.375,” the length code is -6. Lastly, if the fractional length is at 8/16″ (1/2″) and at 0.500″ for decimal inch length, the length code would be -8.

Things change for metric fasteners. If the stud length was 6mm and decimal inch length was 0.236,” then the length code would be -6. For an 8mm stud length and decimal inch length of 0.315,” the length code is -8. Finally, if your stud length reached 10mm and decimal inch length was 0.394,” the length code would be -10.

Imperial

Length CodeFractional LengthDecimal Inch Length
-44/16″ (1/4″)0.250″
-66/16″ (3/8″)0.375″
-88/16″ (1/2″)0.500″

Metric

Length CodeFractional LengthDecimal Inch Length
-66mm0.236″
-88mm0.315″
-1010mm0.394″

Standoffs

The length codes for standoffs are measured in 1/32″ increment for imperial fasteners. Just as with studs, metric standoffs length code is measured in millimeters and is the actual measurement of the fastener.

For imperial if the fractional length is at 10/32″ (5/16″) and decimal inch length is 0.312″ then the length code would be -10. For a fractional length of 12/32″ (3/8″) and decimal inch length of 0.375″ then length code is -12. A length code of 14/32″ (7/16″) and 0.437″ for decimal inch length the length code would come to be -14. Lastly, if the fractional length is long as 16/32″ (1/2″) and decimal inch length of .500″ then length code would come to be -16.

Moving to the metric side of things, if the standoff is 6mm of length and 0.236″ of decimal inch length, the length code is -6. A standoff length of 8mm and decimal inch length of 0.315,” the length code is a -8. Finally, if the standoff length is 10mm and 0.394″ in decimal inch length the length code is -10.

Imperial

Length CodeFractional LengthDecimal Inch Length
-1010/32″ (5/16″)0.312″
-1212/32″ (3/8″)0.375″
-1414/32″ (7/16″)0.437″
-1616/32″ (1/2″)0.500″

Metric

Length CodeFractional LengthDecimal Inch Length
-66mm0.236″
-88mm0.315″
-1010mm0.394″

Conclusion

One handy tip for remembering the parts of a self-clinching fastener code: Just remember the abbreviation STL:

  • Style of Fastener & Material
  • Thread Code
  • Length

Self-clinching fasteners are one of the most useful hardware components at a designer’s disposal. Here at Protocase, we ensure we stock a wide variety of self-clinching nuts, standoffs, studs and other types of fasteners so that you can create, quote and order a design to suit your specific requirements and application.

Got a design question, or an enclosure, part or panel design that you’re ready to move forward with? We’re here to help. Contact us to get connected with your Protocase Account Manager (or go directly to our Request-a-Quote form to get your price quote started).

If you want to learn more about self-clinching fasteners, we’ve got you covered. Check out these links to get an even better understanding:

Finally, if you haven’t already, check out our website for our full list of all of the self-clinching fasteners that we stock at Protocase, as well as options that we don’t stock as inventory, but can order in for additional leadtime and cost.

Happy designing!

About The Author

Christa Carey

Christa Carey has been with Protocase since the very beginning. In fact, she was the first employee the company hired back in 2002, after working for the Protocase co-founders in a previous job. She graduated in 2000 from Cape Breton University in Nova Scotia, Canada. As the CNC Engineering and Design Services Technical Services Manager, Christa manages a team of engineers and technologists in the CNC Machining Division.

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