Press-In Inserts, Rivet Nuts and Threads in Sheet Metal
Choosing between self-clinching PEM inserts, rivet nuts, tapped holes and welded studs for thin sheet metal
Sheet metal thinner than about 3 mm cannot reliably hold a tapped thread under repeated assembly and disassembly, since only 2-3 thread turns engage and the thread strips or the sheet deforms. The standard alternatives are self-clinching inserts (PEM-type), rivet nuts (blind rivet nuts, often called by the brand names Rivnut or Riv-nut), tapped holes with thread inserts, or welded studs, each suited to a different sheet thickness, access condition and load.
This page compares the four methods, gives minimum sheet thickness and pull-out strength guidance, and states which fits common enclosure, bracket and panel designs made in Egypt, the UAE and Saudi Arabia.
The four threading methods compared
Self-clinching inserts (PEM and equivalent) are pressed into a punched or laser-cut pilot hole and permanently clinch into the sheet under press force, displacing metal into a knurled or grooved insert body. They need one-sided access, install in seconds on a press, and give a strong, flush or protruding thread suited to repeated bolt cycling, but the sheet must be soft enough to cold-flow around the insert (mild steel, aluminium, stainless in thinner gauges).
Rivet nuts are installed from one side using a setting tool that pulls the insert body to collapse and clamp it against the back of the sheet, so they work where the back face is inaccessible after assembly (closed box sections, tubes). They tolerate thinner sheet than a clinch insert in some cases but generally give lower pull-out strength for the same thread size.
| Method | Minimum sheet thickness | Access needed | Typical pull-out (M5) | Install method |
|---|---|---|---|---|
| Self-clinching insert (PEM) | 1.0 mm | One side, insert pressed from back | 3.5-5 kN | Arbor press |
| Rivet nut (blind) | 0.8 mm | One side only, fully blind | 2.5-4 kN | Hand or pneumatic setting tool |
| Tapped hole (direct thread) | 3.0 mm minimum, 5 mm recommended | Access to tap from one side | Depends on thread engagement | Tap and die, or CNC tapping |
| Welded stud | any, limited by weld heat distortion | One side, welder access | Exceeds thread strength, weld-limited | Stud welding gun |
Choosing by application
For sheet metal enclosures and panels under 3 mm that need a reusable bolted connection (covers, access doors, mounting brackets), a self-clinching insert is the standard choice when both sides of the sheet are reachable during assembly, since it gives the strongest, most consistent thread of the thin-sheet options. Where the insert must be installed after the box is welded closed, or where only one side will ever be accessible, a rivet nut is the correct substitute despite its slightly lower pull-out strength.
Direct tapping is reserved for plate 5 mm and thicker, where enough thread engagement exists without an insert; tapping thinner material gives a thread that strips after a handful of cycles. Welded studs suit structural or high-load attachment points where the stud itself, not a female thread, is the fastening feature, such as mounting brackets that bolt through from the opposite side.
- Removable access panels and covers under 3 mm: self-clinching insert
- Closed box sections, tube frames, blind assembly: rivet nut
- Structural plate 5 mm and above: direct tapped thread
- High-load stud attachment, opposite-side bolting: welded stud
- Stainless enclosures needing corrosion-matched inserts: stainless self-clinching insert, not zinc-plated steel
Installation and material compatibility
Self-clinching inserts are available in steel (zinc plated), stainless steel and aluminium bodies; matching the insert material to the sheet material avoids galvanic corrosion, so a stainless insert should go into stainless sheet, and an aluminium insert into aluminium sheet. Installing an insert requires a flat-bottomed pilot hole of the correct diameter (specified by the insert manufacturer per thread size) and squareness within about 0.1 mm to seat correctly; laser-cut pilot holes meet this without secondary operations.
Rivet nuts are less sensitive to installation squareness but need clearance behind the sheet for the collapsing body, so wall thickness and internal clearance inside a box section must be checked against the rivet nut's grip range before specifying.
Worked example
An electrical enclosure door, 1.5 mm mild steel, needs 6 removable M5 bolted points to a frame that will be closed after welding: rivet nuts are specified in the frame because the back face becomes inaccessible once the box is welded shut, while self-clinching inserts are used in the door panel itself, which is accessible from both sides before final assembly. Both give adequate pull-out strength (2.5-5 kN) for a door that will be opened and closed hundreds of times over the enclosure's service life.
Design tips
- Specify insert material to match the sheet (steel insert in steel sheet, stainless in stainless, aluminium in aluminium) to avoid galvanic corrosion at the joint.
- Do not tap threads directly into sheet under 3 mm for anything that will be bolted and unbolted more than a handful of times; use an insert instead.
- Call out the insert pilot hole diameter from the manufacturer's data sheet on the drawing, not just the thread size, since it is not the same as the bolt's clearance hole.
- For blind assemblies (closed box sections), specify rivet nuts and confirm the internal clearance behind the sheet matches the rivet nut's grip range.
- Where flush mounting matters (a panel that must sit perfectly flat against another surface), specify a flush-type self-clinching insert rather than the standard protruding-head type.
- For coastal or humid environments, specify stainless self-clinching inserts even in a mild steel sheet enclosure if the enclosure itself will be powder coated, since the insert thread is often left exposed and unpainted.
- State the expected number of assembly cycles on the RFQ; this changes whether a direct tapped thread in thicker plate is acceptable versus needing an insert.
Applications
| Industry | Example parts | Typical fastening method |
|---|---|---|
| Electrical enclosures | Access doors, panel covers | Self-clinching insert, rivet nut in closed sections |
| Machinery and OEM parts | Covers, guards, access panels | Self-clinching insert |
| HVAC and ducting | Access doors, damper frames | Rivet nut |
| Furniture and interior fit-out | Panel joints, bracket mounts | Self-clinching insert |
| Automotive aftermarket | Brackets, trim panels | Rivet nut, self-clinching insert |
| Signage and architectural | Panel-to-frame mounting | Rivet nut |
| Structural steelwork | Base plates, connection points | Direct tapped thread, welded stud |
Pricing and lead time
Cost is driven by fastener count and type (self-clinching inserts and rivet nuts each add a per-piece material and installation cost on top of the base part), by material match (stainless inserts cost more than zinc-plated steel and are specified for corrosion-matched or coastal applications), and by installation method (press-installed inserts on a laser-cut pilot hole are faster per piece than field-installed rivet nuts with a hand tool). Adding inserts or rivet nuts to a standard sheet metal part typically adds 1-2 working days to lead time depending on quantity, since it is a secondary operation after cutting and forming.
Frequently asked questions
Not reliably for anything bolted more than a few times; 2 mm gives only 2-3 thread turns, which strips under normal torque and repeated cycling. Use a self-clinching insert instead.
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