Rivnut vs PEM Nut

Both a rivnut and a PEM nut give you a threaded hole in material too thin to tap. The difference that actually decides it is access: a PEM nut needs a press on both sides of the sheet, and a rivnut does not. That single fact is why rivnuts work on tube and closed sections where PEM hardware cannot go at all.

If you can reach both faces of a flat sheet, a PEM nut is usually the simpler choice. If you cannot, a rivnut may be your only option that still gives you real threads.

How each one installs

A PEM nut, generically a self-clinching nut, sits in a precisely sized hole, and a press squeezes it until the knurled shoulder displaces sheet metal into an undercut in the fastener. The sheet itself locks the nut in place. That takes a press with clearance above and below the hole.

A rivnut, also called a rivet nut or blind rivet nut, is a threaded rivet. It goes in from the front, and a tool pulls a mandrel through the threads to bulge the back of the body out into a flange behind the sheet. The part is clamped between the head at the front and that bulge at the back. Everything the tool needs is on one side.

When to use a rivnut

• Tube parts. You cannot get a press inside a closed tube, so self-clinching hardware is out.
• Closed or boxed assemblies where the back of the sheet is unreachable after forming or welding.
• Parts that get threads after assembly, when the sheet is no longer a flat blank.
• Pull-out loads in thicker sheet. A rivnut clamps the material between its head and the collapsed body, so its grip grows with thickness. In thicker material it will generally out-hold a comparable PEM nut on pull-out.

When to use a PEM nut

• Flat sheet you can press. This is most sheet metal parts, and a PEM nut is the simpler, lower profile choice when you can reach both sides.
• A flush surface. Flush nuts finish level with the sheet face. Rivnuts leave a head proud of the surface and a bulged flange behind it.
• Anything besides a plain thread. Studs, standoffs, and blind standoffs have no rivnut equivalent.

Grip range

This is the detail that catches people out, and it has no PEM equivalent. A rivnut only clamps correctly across a specific material thickness, called its grip range, and each size is stocked in more than one range. A #6-32 rivnut comes in a 0.020" to 0.080" version and a 0.080" to 0.130" version. Use the thin-material one in 0.125" sheet and the mandrel will not form a proper flange.

A PEM nut has a minimum sheet thickness and otherwise does not care. A rivnut has to be matched to your material.

Rivnut sizes and materials

Rivnuts are a hardware option in Hole Ops, in both inch and metric threads:

• Inch: #6-32, #8-32, #10-24, #10-32, 1/4-20, 5/16-18, 3/8-16
• Metric: M4x0.7, M5x0.8, M6x1.0, M8x1.25, M10x1.5

They are available in aluminum, steel, galvanized steel, and stainless steel. Stainless costs noticeably more per insert than the other three, so it is worth confirming you need it.

Thickness support depends on thread size. The smallest inch sizes start at 0.020" material, and the larger sizes reach about 0.312". Every current size and grip range is listed on the hardware guidelines page.

Tube parts

Tube is where rivnuts earn their place, and it comes with two hard rules worth designing around:

1. Only taps and rivnuts are available on tube parts. No other hardware can be installed.
2. Rivnuts install from the outside of the tube, never from inside it.

Keep rivnut holes on flat faces, at least one wall thickness from any edge or end cut. On square and rectangular tube, stay off the outside corner radius.

Quick comparison

Adding rivnuts to a quote

Automatic hardware detection is not yet available for rivnuts, so add them in the quoting software.

Upload the STEP or DXF, click the hole you want threaded, filter by hardware type, choose Rivnut, and pick the size. Fabworks resizes the hole for the insert.

For the rest of the hardware lineup, see the hardware guidelines. To have PEM hardware added to your quote automatically, see how to auto-add PEM hardware from your CAD model.