M8 rivet nuts are commonly used for stronger mounting points in sheet metal, brackets, racks, equipment panels, vehicle builds, trailers, and fabricated assemblies. They provide an M8 internal thread where the back side of the material is difficult or impossible to access.
The most important part of the installation is drilling the correct hole. If the hole is too small, the insert may not seat correctly. If the hole is too large, the rivet nut can spin or pull out.
Quick Answer
Many standard M8 rivet nuts use a hole around 11 mm, but this is not universal. Some M8 body styles, especially half-hex, large-flange, or specialty inserts, may require a larger hole.
Always check the exact manufacturer’s datasheet before drilling the final panel.
Common M8 Rivet Nut Hole Size
| Thread Size | Common Hole Size | Closest Inch Size | Notes |
|---|---|---|---|
| M8 x 1.25 | Around 11 mm | Around 7/16 in | Common for some standard M8 inserts |
| M8 specialty/hex styles | May be larger | Varies | Check the exact part |
An M8 thread does not automatically mean every M8 rivet nut uses the same drill size. The outside diameter of the rivet nut body determines the hole size, not just the internal thread.
M8 Rivet Nut Drill Bit Size
For many M8 rivet nuts, an 11 mm drill bit is a common starting point. In imperial drill sizes, 7/16 inch is close to 11.1 mm.
However, do not assume 7/16 inch is correct for every M8 rivet nut. Some inserts require a larger hole, especially if the body is hex-shaped or oversized.
Best practice:
- Check the supplier’s recommended hole size.
- Drill a test hole in scrap material.
- Insert the rivet nut by hand.
- Make sure the flange sits flat.
- Set the rivet nut and check that it does not spin.
Why M8 Rivet Nut Hole Sizes Vary
M8 rivet nut hole sizes vary because different inserts have different outside body diameters.
The required hole may change depending on:
- Round body or hex body
- Smooth body or knurled body
- Open-end or closed-end design
- Flat head or countersunk head
- Standard flange or large flange
- Steel, stainless steel, or aluminum construction
- Grip range
This is why one M8 rivet nut may fit an 11 mm hole, while another M8 insert may require a larger hole.
M8 Rivet Nut Grip Range
Grip range is the material thickness range that the rivet nut is designed to clamp. An M8 rivet nut may be available in several grip ranges.
Before installing, check the thickness of the panel or bracket. If the material is outside the rivet nut’s grip range, the insert may not collapse correctly.
Common problems caused by the wrong grip range include:
- Insert spins after installation
- Insert pulls out under load
- Flange does not sit flat
- Bulb does not form correctly behind the panel
- Bolt feels loose even after tightening
M8 Rivet Nut Installation Torque
Be careful with torque values for M8 rivet nuts. There are two different torque-related issues:
- The force or stroke used to install the rivet nut
- The tightening torque applied to the bolt after installation
These are not the same thing.
The installation tool needs to collapse the rivet nut enough to grip the material, but over-setting can damage the insert or panel. Under-setting can leave the insert loose.
The final bolt torque depends on the insert material, parent material, bolt grade, thread condition, lubrication, and application. Do not use a generic bolt torque chart without considering the installed rivet nut and panel material.
Common M8 Rivet Nut Installation Mistakes
Hole Too Large
An oversized hole is one of the main reasons M8 rivet nuts spin. The insert needs enough contact with the hole wall to resist rotation.
Hole Too Small
If the hole is too small, the rivet nut may scrape, deform, or fail to sit flat. Forcing the insert into the hole can damage the body before installation.
Wrong Grip Range
Even with the right hole size, the installation can fail if the material is too thin or too thick for the rivet nut.
Over-Setting the Rivet Nut
Too much tool force can distort the rivet nut, damage threads, or deform thin material.
Under-Setting the Rivet Nut
Too little setting force can leave the rivet nut loose. It may feel acceptable at first but spin when the bolt is tightened.
Using the Wrong Body Style
Round-body rivet nuts may not be ideal for every application. Hex or knurled body inserts can offer better spin resistance when installed in the correct hole.
Should You Use M8 or M6?
M8 is stronger than M6 in many applications, but it also requires a larger hole and more installation force. If the material is thin, soft, or narrow, M6 may be easier to install cleanly.
Use M8 when you need a larger bolt, stronger fastening point, or heavier-duty mounting surface. Use M6 when space is limited or the load is lighter.
Related Guides
- M6 Rivet Nut Hole Size & Torque Guide
- M5 Rivet Nut Hole Size Guide
- Rivet Nut Hole Size Chart
- Why Rivet Nuts Spin and How to Fix Them
- Rivet Nut Grip Range Explained
FAQ
What size hole do I drill for an M8 rivet nut?
Many M8 rivet nuts use a hole around 11 mm, but some styles require larger holes. Check the exact part before drilling.
Is 7/16 inch close to 11 mm?
Yes. 7/16 inch is about 11.1 mm, so it is close to 11 mm. However, you should still check the recommended hole tolerance for the insert.
Why does my M8 rivet nut spin?
The most common causes are an oversized hole, wrong grip range, under-setting, soft material, or using a body style that does not provide enough spin resistance.
Can I install an M8 rivet nut in thin sheet metal?
Yes, but only if the rivet nut’s grip range matches the material thickness. Thin material may require a specific low-grip insert.
Are all M8 rivet nuts the same hole size?
No. M8 refers to the internal thread size. The required hole size depends on the outside body of the rivet nut.