Rivet Nuts: How a Threaded Rivet Solves Thin-Sheet Jointing
Executive Summary
To screw an M6 bolt into 1 mm sheet metal, the three conventional approaches all run into a wall: tapping cannot hold the thread, welding a nut burns through the zinc layer and warps the panel, and the back side is simply unreachable. A rivet nut lodges the thread inside a single part, enabling single-sided installation in about 3 seconds with a permanent fix. This article explains its working principle, size system and typical application boundaries.
Table of Contents
An M6 Thread in 1 mm Sheet Metal
When making an electrical box, cabinet liner or battery-pack end plate, the common condition is this: the sheet is only 1 mm to 2 mm thick, but structurally it must carry the joint load of an M6 bolt. The designer faces three choices, each with a fatal flaw.
Approach 1: Tap the Sheet Metal Directly
Tapping an M6 internal thread in 1 mm sheet gives an engagement length of only about 1.5 turns, while the M6 coarse pitch is 1 mm, so in reality only one or two threads are loaded. By experience, the reasonable engagement length for a steel bolt in a soft thin sheet should be above 1.8d, about 11 mm. 1 mm sheet is nowhere near that fraction; a slight over-torque pulls the thread right out.
Approach 2: Weld a Nut
Welding brings two secondary problems: first, the welding heat input burns through the zinc coating, so the area around the weld loses corrosion protection and rust starts at the weld; second, welding heat warps the panel, once panel flatness is destroyed, the mating seals, panels and covers no longer fit tightly. In addition, a weld nut requires double-side work—someone or something must reach the back.
Approach 3: Add a Nut on the Back Side
This is the most primitive and most reliable approach—but only if a hand or tool can reach the back. For positions inside closed profiles, tubes and enclosed cavities, the back is simply unreachable. At that point the design reaches an impasse.
The Rivet-Nut Approach
A rivet nut (also called a blind rivet nut, a single-sided form of press-in nut) works very directly: build the thread into a single part, then rivet that part onto the thin sheet.
Installation Principle
- Drill a round hole of the specified diameter in the sheet (usually just a punched or drilled hole);
- Pass the rivet-nut body through the hole, with the head against the panel;
- Using a rivet tool from the same side, pull the mandrel inside the nut so the body deforms plastically on the back side of the sheet, flaring outward into a large-diameter clinching flange;
- The clinching flange and the head flange clamp the sheet between them, forming a permanent mechanical lock;
- Break off the mandrel, withdraw the tool, and installation is complete.
The whole process is single-sided operation, completed in about 3 seconds, with no back-side contact, no welding heat source and no tapping of the sheet.
Comparison with Weld Nuts and Press-In Nuts
| Comparison | Rivet Nut | Weld Nut | Press-In Nut |
|---|---|---|---|
| Working side | Single-sided | Double-side reach needed | Usually double-side pressing |
| Heat source needed | No | Welding needed | No |
| Damage to coating | None | Burns through coating; needs touch-up | None |
| Panel deformation | Slight, controllable | Obvious heat distortion | Small |
| Applicable sheet thickness | About 0.5–6 mm | Wide range | Needs enough thickness to grip |
| Removability | Basically non-removable | Non-removable | Non-removable |
| Cycle time per piece | About 3 s | Tens of seconds | About 2–5 s |
| Back-side protrusion | Clinching flange protrusion | Weld spot protrusion | Bulge |
The selection logic is clear: where the back is reachable, the sheet is thick enough and volumes are high, press-in is most economical; where the back is unreachable or higher sealing is needed, the rivet nut is the first choice; welding is considered only for thick structural sheets where later corrosion remediation is acceptable.
Size System and Material Selection
Common Size Range
| Thread Size | Applicable Sheet Thickness (Ref.) | Typical Use |
|---|---|---|
| M3 / M4 | 0.5–2.0 mm | Electronic chassis, control panels, small sheet-metal parts |
| M5 / M6 | 1.0–3.5 mm | Cabinets, electrical boxes, air-conditioner housings |
| M8 / M10 | 1.5–6.0 mm | Structural parts, brackets, load-bearing joints |
| M12 and above | Above 3.0 mm | Heavy structures, load-bearing joints |
Materials and Surface Treatment
- Carbon steel: high strength, low cost; needs galvanizing or zinc-nickel corrosion protection. Suitable for general structures and indoor environments.
- Stainless steel (304 / 316): good corrosion resistance; suited to outdoor, humid, water-contact and food/medical environments. 316 is used for marine and chemical environments.
- Aluminum alloy: light weight, used where weight matters. Lower strength than same-size steel products; re-check by load when selecting.
- Brass: good conductivity, stable friction characteristics; used for electrical connections and where good contact is needed.
Typical Application Scenarios
| Industry | Typical Location | Problem the Rivet Nut Solves |
|---|---|---|
| Electrical control & distribution | Cabinet side panels, doors, mounting plates | Inside closed profiles is unreachable; single-sided installation solves accessibility |
| New energy | Battery-pack end plates, tray edge beams, box covers | Avoid welding damage to coating and sealing faces; maintain flatness |
| Rail transit & commercial vehicles | Car liners, side skirts, equipment bay covers | Outdoor and humid environments; stainless models meet corrosion requirements |
| Machinery & automation | Equipment sheet-metal housings, guards, rail mounting plates | No tapping, no welding; improves assembly cycle time |
| Appliances & commercial equipment | Housing fixing, handle and hinge mounting | Thin sheet gains a thread that withstands repeated assembly |
Four Things to Confirm at the Design Stage
- Sheet material and thickness: determines the selectable size range and hole parameters. If the thickness is outside the applicable range, clinching is insufficient (not clamped) or the body protrudes too far (interfering with back-side parts).
- Hole diameter and tolerance: the rivet-nut hole is the load-bearing interface. If too large, the clinching flange cannot grip effectively; if too small, it cannot be fitted or the sheet hole deforms. The hole diameter must be machined to the specified value for the selected model; empirical values from other sizes cannot be reused.
- Back-side space: after clinching, a protruding flange forms on the back; its protrusion height must be less than the space behind it to avoid interference with other parts. This is the most easily missed item.
- Joint load and number of disassembly cycles: determines thread size and material choice. Positions needing frequent disassembly should use higher-strength stainless-steel or steel models.
The value of a rivet nut is not just "no welding needed." It turns thin-sheet jointing from a solution dependent on a process (welding) and assembly accessibility (double-side work) into a solution that can be fully calculated at the product design stage: where the hole is, how large it is, how thick the sheet is, and how much space to leave behind—all defined by the drawing.
Conclusion: Put the Thread Inside One Part
The difficulty of thin-sheet jointing is essentially that the condition "thin" simultaneously destroys the engagement length of the thread and the assembly accessibility of the joint. The rivet-nut solution peels the thread off the sheet and builds it into an independent, rivetable part, so the designer no longer has to compromise for sheet thickness and hand access.
YF Zhichengjia supplies rivet nuts, rivet studs and other riveting products along with matching installation solutions, covering carbon-steel, stainless-steel and aluminum-alloy materials and common thread sizes, and can provide matching advice based on sheet thickness and hole type—helping clinching parameters be settled at the drawing stage rather than discovering the hole was wrong only during trial assembly.
