What Is PEM Hardware?
PEM (Penn Engineering & Manufacturing) hardware refers to a family of self-clinching fasteners designed to be permanently installed into sheet metal. They create strong, reusable threads in materials too thin to tap — typically 0.040″ to 0.125″ thick.
Unlike weld nuts or rivnuts, PEM fasteners are pressed into the sheet during fabrication, becoming flush or near-flush with the surface. The result is a clean, permanent threaded attachment point that won’t spin, pull out, or interfere with the opposite side of the panel.
Types of PEM Fasteners
Self-Clinching Nuts (CLS, CLSS, SP)
The most common type. A knurled collar is pressed into a pre-punched hole in the sheet metal. The displaced material flows into the knurl, locking the nut permanently in place. Available in carbon steel (CLS), stainless steel (CLSS), and aluminum (SP).
- CLS — Carbon steel, for use in steel sheets ≥ HRB 70
- CLSS — Stainless steel, for stainless sheets
- SP — Stainless steel, for aluminum and softer sheets
Self-Clinching Studs (FH, FHS, FHA)
Male threaded fasteners that install the same way. The head clinches into the sheet, leaving a protruding stud ready for a mating nut. Used when you need a bolt sticking out of a panel rather than a threaded hole in it.
Self-Clinching Standoffs (SO, SOS, SOA)
Threaded or unthreaded spacers that clinch into the parent sheet and hold a second panel or PCB at a fixed distance. Common in electronics enclosures where circuit boards mount to a chassis.
Broaching Nuts and Studs
Designed for blind-side installation — they press in from one side only, useful when you can’t access the back of the sheet. The serrated body bites into the hole wall rather than displacing material on the far side.
Floating Fasteners
Self-clinching nuts or studs that allow lateral movement (typically ±0.030″ to ±0.060″) to compensate for hole misalignment between mating panels. Invaluable in enclosures and rack-mount equipment.
When to Use PEM Hardware
- Thin sheet metal — Material too thin to tap reliable threads (generally under 0.090″)
- Flush surfaces — Where weld nuts or rivnuts would protrude unacceptably
- Repeated assembly/disassembly — PEM threads handle dozens of cycles without degradation
- Clean aesthetics — No weld marks, no deformation on the show side
- Pre-painted or powder-coated panels — Install before finishing; weld nuts would burn the coating
- Aluminum and stainless — Where welding is difficult or undesirable
PEM vs. Alternatives
| Feature | PEM | Weld Nut | Rivnut | Tapped Hole |
|---|---|---|---|---|
| Min. sheet thickness | 0.040″ | 0.048″ | 0.020″ | 3× thread pitch |
| Flush mount | Yes | No | Partially | Yes |
| Torque resistance | High | Very high | Moderate | Low in thin sheet |
| Pushout resistance | High | Very high | Moderate | N/A |
| Tooling required | Press or C-frame | Welder | Rivnut tool | Tap |
| Works in aluminum | Yes | Difficult | Yes | Weak threads |
| Post-finish install | Before or after | Before only | After | Before or after |
Installation
PEM installation is simple but must be done correctly:
- Punch or drill the mounting hole to the spec diameter (see PEM catalog — every part number has a specific hole size)
- Place the fastener in the hole from the accessible side
- Apply a parallel squeezing force using a press, C-frame, or insertion tool — never hammer them in
- Verify the fastener is flush and doesn’t rotate under torque
Critical: The sheet metal must be softer than the fastener. Installing a carbon steel PEM nut into hardened steel won’t work — the knurl can’t displace the parent material. Match the fastener material to the sheet:
- Steel PEM → Steel sheet (HRB 70+)
- Stainless PEM → Stainless sheet
- Stainless PEM (SP series) → Aluminum sheet
Design Tips
- Edge distance: Maintain at least 2× the fastener head diameter from any edge or bend
- Hole tolerance matters: Too large and the fastener won’t clinch; too small and it won’t seat
- Specify on drawings: Call out the PEM part number, hole size, and installation side — don’t assume the fabricator will figure it out
- Test pull-out and torque-out: For critical applications, specify minimum pushout force (lbs) and torque-out resistance (in-lbs)
- Consider floating hardware for multi-panel assemblies — it saves hours of alignment headaches
Common Pitfalls
- Wrong material combo — Aluminum PEM in steel sheet = no clinch. Always check hardness compatibility.
- Hole too large — The fastener drops through or spins freely. Follow the catalog spec exactly.
- Insufficient press force — Under-pressed PEMs will spin out under load. Use the recommended installation force.
- Installing after powder coat — The coating thickness changes the effective hole size. Account for 0.002″–0.005″ per side.
Bottom Line
PEM hardware is the professional standard for threaded fastening in sheet metal fabrication. When the design calls for clean, reliable, reusable threads in thin material, self-clinching fasteners are almost always the right answer. Specify them on your drawings, call out the part numbers, and your fabricator will thank you.