An M6 rivet-nut is a simple solution for adding strong, M6 threads to thin materials like sheet metal, tubing, or plastics. Because it’s a blind fastener, you can install it from one side without needing access to the back of the material.
To ensure a reliable installation, getting two things right is crucial:
- Hole Size: An incorrect hole size can lead to the rivet-nut spinning in place (spin-out) or pulling through the material (pull-through).
- Assembly Torque: Applying too much torque can crush the panel, while too little results in an unreliable or loose connection.
This guide provides easy-to-read charts for hole diameters, metric and imperial drill bit conversions, and torque specifications. With these references, you can correctly spec and install M6 rivet-nuts on your first try, ensuring a secure and durable assembly.
Quick Specs (at a Glance)
For readers who just need the numbers.
| Spec | Typical Value / Range | Notes |
| Recommended hole Ø for M6 round-body | ~9.0 mm (common), ≈8.8–9.2 mm depending on body style & brand | Böllhoff RIVKLE® M6 lists 9.0 mm drill; POP/RS product pages also specify 9 mm for M6. Tighter/looser fits depend on material and insert style. (https://eshop.boellhoff.de/) |
| Nearest drill equivalents | 11/32″ (8.73 mm) = slightly tight; 23/64″ (9.13 mm) = slightly loose | Choose based on fit, parent material, coating, and body style; ream if roundness matters. (Misumi) |
| Assembly torque for M6 screw into rivet-nut | Al body: ~9.5 N·m; Steel/Stainless body: ~11 N·m (with class 8.8 or A2-70 hardware) | Manufacturer recommended tightening torques for M6 joints; always pilot-test in your stack-up. (dejondfastening.com) |
| Example torque-to-turn (spin-out) thresholds | Round shank in steel plate: ~7 N·m; Hex shank: >21 N·m | Representative Tubtara® test values showing why hex/knurled bodies resist rotation better. |
What Is an M6 Rivet-nut?
- A blind, threaded insert that adds durable M6 internal threads to thin or hollow sections when you can’t access the backside.
- Common body styles: smooth round, knurled, half-hex/full-hex, keyed, closed-end—chosen for anti-rotation and sealing needs.
- Typical applications: automotive upfitting, racks/enclosures, aluminum extrusions, composites.
- Thread tolerance is commonly ISO 6H and mates with commercial 6g screws (check the specific catalog page for your part).
Choosing the Correct Hole Size (Step-by-Step)
- Measure total stack thickness (material + coatings).
- Match a grip range so the insert collapses correctly across that stack.
- Pick a body style for the parent material (round vs knurled vs hex).
- Set the hole Ø from the exact part’s datasheet (catalog first, then drill/ream).
- Pilot test in scrap to validate collapse profile and spin resistance.
Why ranges vary: Different families (e.g., slotted/“plus-nut” styles vs. standard round) publish different hole diameters for M6. Standard round bodies commonly specify ~9.0 mm; slotted/plus-style inserts are often a hair tighter (≈8.9 mm)—always follow the specific OEM table for your chosen insert.
Hole Size Reference (Examples)
| M6 Insert Family | Typical Hole Ø (mm) | Notes |
| Standard round / knurled | ~9.0 (often 9.0–9.2) | General-purpose; more sensitive to hole roundness/finish. Examples show 9.0 mm drill for RIVKLE® M6; POP/RS pages list 9 mm. (https://eshop.boellhoff.de/) |
| Plus-Nut / slotted styles | ≈8.9 (series-specific) | Wider backside footprint for thin/soft materials; check the exact series datasheet for drilling diameter. (boellhoff.com) |
| Hex-body | Hex-punched aperture | Highest anti-rotation; requires hex hole/broach. Performance tables show much higher torque-to-turn than round bodies. (Sherex Fastening Solutions) |
Tip: If you’re torn between 11/32″ and 23/64″, weigh parent material hardness and coating thickness. Tighter holes improve spin resistance but can bind after coating; looser holes ease insertion but reduce torque-out. Validate on scrap before production.
Drill Equivalents for M6 Rivet-nut Holes
For most M6 rivet-nut families, the catalog hole diameter clusters around 9.0 mm, with acceptable tolerance windows typically spanning ≈ 8.9–9.2 mm depending on body style (round, knurled, hex) and the specific brand/series. Böllhoff’s RIVKLE® tables, for example, list d = 9.0 mm for several M6 variants.
If you’re working from an imperial drill index, here are the closest fractional and letter equivalents you’ll actually find in a shop drawer:
| Target metric | Fractional (inch → mm) | Letter (inch → mm) | Fit comment |
| 8.9 mm | 11/32″ = 0.3438″ → 8.73 mm | S = 0.348″ → 8.84 mm | Both are close; 11/32″ runs a touch tight, S is a hair looser. (icscuttingtools.com) |
| 9.0 mm | (no exact fractional) → nearest 23/64″ = 0.3594″ → 9.13 mm | T = 0.358″ → 9.09 mm | T is very close to 9.0 mm; 23/64″ is ~0.13 mm oversize. (icscuttingtools.com) |
| 9.1–9.2 mm | 23/64″ = 9.13 mm | T = 9.09 mm | Both land in the common 9.1–9.2 mm “looser” tolerance band. (icscuttingtools.com) |
How to choose in the real world
- Tighter hole (≈ 8.9–9.0 mm): maximizes spin resistance for smooth/knurled round bodies in clean sheet metal. Great when panel is uncoated or you can ream after drilling. If coating thickness or burrs are present, this can become too tight.
- Looser hole (≈ 9.1–9.2 mm): gives you breathing room for paint/powder, slightly out-of-round holes, or knurled/hex bodies that still achieve high torque-to-turn thanks to geometry.
- Hex-body inserts: often require a hex aperture (punched/broached). Don’t substitute a round 9 mm hole—the performance assumptions change. Follow the specific series drawing.
Process tips
- Step-drill to within ~0.3 mm of target, then finish with the final bit/reamer to keep holes round and burr-free.
- If hole quality matters (e.g., thin aluminum or higher service torque), use a reamer to hit a consistent final size; letter T reamers track nicely to 9.09 mm when you’re targeting a nominal 9.0 mm fit. (littlemachineshop.com)
- Always compare your chosen drill to the exact datasheet for the insert series you’re installing—M6 families differ (e.g., plus-nut/slotted types vs. standard round).
M6 Torque: Assembly vs. Spin-Out vs. Max Torque
Correct torqueing keeps clamp load where you need it without damaging the insert or the parent material. It helps to separate three numbers:
- Assembly torque — what you tighten the screw to in service.
- Torque-to-turn (spin-out) — the torque where the insert starts rotating in the panel.
- Max torque — the maximum torque the installed insert can sustain before thread or body failure in a standardized test.
Assembly Torque (what you tighten the screw to)
Start with conservative assembly torque and validate in scrap that matches your stack thickness and material.
| Insert material | Recommended M6 assembly torque (N·m) | Compatible hardware |
| Aluminum | ~ 9.5 | Class 8.8 / A2-70 |
| Steel / Stainless | ~ 11 | Class 8.8 / A2-70 |
These are manufacturer reference values for blind rivet-nut joints (rule-of-thumb for common service conditions). Adjust downward for lubrication and pay attention to coatings and joint friction. Always pilot-test in your application.
Spin-Out (Torque-to-Turn) & Max Torque (insert limits)
Representative M6 values (tested in steel plate, mid-grip) illustrate why body style matters:
| Body style (M6) | Torque-to-turn (spin) | Max torque | Takeaway |
| Round shank | ~ 7.0 N·m | > 19.0 N·m | Adequate in many metals; more sensitive to hole quality and fit. |
| Hex shank | > 21.0 N·m | > 24.5 N·m | Big jump in anti-rotation; better for higher service torque/vibration. |
Values per Tubtara® technical data (bolts class 8.8 used in tests). Real parts vary by series/material—always check the sheet for your exact insert.
Rule of thumb: Keep your assembly torque comfortably below both the spin-out and max-torque thresholds for the insert/stack you’re using. If your validated assembly torque approaches the spin-out number—or if you see any rotation during testing—drop the torque or upgrade the body (knurled, keyed, or hex), and revisit the hole size/roundness and grip range.
Related spec note: Böllhoff’s RIVKLE® HRT pages also show why material pairings and insert design affect allowable loads and installation settings; treat any single torque table as a starting point, not a blanket rule.
Comparison — Body Styles & When to Use Them
| Body Style | Hole Prep | Spin Resistance | Best For | Watch-outs |
| Smooth round | Standard round hole | ★★☆☆☆ | General sheet metal, coated panels | Sensitive to oversize or out-of-round holes; verify hole quality and grip range. |
| Knurled round | Standard round hole | ★★★☆☆ | Aluminum or painted panels (more bite) | Some catalogs call for a slightly looser hole to allow knurls to engage; mind coating thickness. |
| Half-hex / full-hex | Hex hole | ★★★★☆ to ★★★★★ | Higher torques, vibration, service environments with frequent fastener cycling | Requires punch/broach; tighter positional tolerances and edge distance. |
| Keyed | Round hole + keyway | ★★★★☆ | Situations where anti-rotation is critical (thin, coated, or low-friction surfaces) | Adds a machining step; plan key orientation for assembly. |
| Plus-Nut (slotted) | Round hole | ★★★☆☆ (by footprint) | Thin/soft materials, composites, large backside bearing area | Larger bulbing; check edge distances and keep-out zones for backside expansion. |
Performance trends supported by OEM engineering data and catalogs.
Material Choices & Galvanic Considerations
- Insert materials: aluminum, steel, stainless—match to the parent material and service environment. Aluminum inserts save weight and resist corrosion in mild environments; steel provides higher strength; stainless maximizes corrosion resistance but can gall without lubrication.
- Coatings & friction control: zinc and ZnNi are common on steel bodies; stainless variants may include passivation or specialty dry-film lubricants (e.g., “low-friction” coatings such as Gleitmo/Seal-type finishes) to reduce galling when paired with stainless screws.
- Galvanic pairs: avoid severe potential differences (e.g., stainless in bare aluminum near salt exposure) or isolate the joint using nylon/phenolic washers, barrier pastes, painted/coated holes, or sealants. Where dissimilar metals are unavoidable, prioritize isolation and periodic inspection.
Real-World Use Cases (and what to spec)
- Automotive / van upfits: Hex-body or knurled M6 in ~1–3 mm steel; start with a ~9.0 mm hole for round bodies (follow the insert’s datasheet), and tighten M6 service screws around ~11 N·m dry when compatible with the insert and joint. Validate on scrap for spin-out and clamp load.
- Aluminum enclosures / extrusions: Knurled or hex-body inserts improve anti-rotation in softer materials. Consider 9.0–9.2 mm holes to account for paint/powder; target ~9.5 N·m assembly torque for M6 with aluminum-body inserts (or per the insert’s torque guidance).
- Composite panels: Plus-nut/slotted styles spread load and reduce pull-through. Drill to the OEM hole spec for the exact series (M6 often lands ~8.9–9.9 mm depending on model and grip), and confirm backside clearance for bulging.
Standards & References (What actually governs this)
- Bolt/nut property classes & tightening torques: ISO 898-1 / ISO 898-2 underpin the strength classes (e.g., 8.8, A2-70) and the tightening limits reflected in many rivet-nut catalogs.
- Aerospace rivet-nuts: NAS 1329 (flat head) and NAS 1330 (countersunk) define qualified round-body blind rivet-nuts used in aviation; useful if you need spec-driven language and controlled performance envelopes.
- OEM engineering data: Tubtara®/Böllhoff and other manufacturers publish mechanical properties, torque-to-turn (spin-out), tightening torque, and grip ranges—always pull the exact datasheet for your selected insert series and verify in your own stack-up before production.
How to Validate in Your Application (Mini Procedure)
Validation is where you turn catalog specs into a reliable joint for your materials and stack-up. Here’s a quick, repeatable procedure you can run on scrap before committing to production.
- Drill to the catalog hole Ø; deburr & degrease.
- Use the exact hole diameter specified for the M6 rivet-nut series you selected.
- After drilling, deburr both sides so the flange sits flat and the shank collapses cleanly.
- Wipe the hole with solvent to remove coolant, oil, or powder overspray. Residue lowers friction and can encourage spin.
- Install an M6 rivet-nut in scrap that matches your stack thickness.
- Stack = base material + coatings + any washers/shims.
- Set the tool’s stroke/pull per the insert’s datasheet; make 1–2 test sets and inspect the collapse profile (uniform bulbing, flange fully seated, no crushing).
- If you’re near the edges or a bend, confirm you maintain the minimum edge distance recommended by the manufacturer.
- Test spin-out while clamping the panel, then verify your assembly torque margin.
- Clamp the test coupon in a vise (or fixture) to simulate service restraint.
- Thread in an M6 screw (same class and lubrication you plan to use), then torque slowly with a calibrated wrench.
- Note the torque where the insert begins to rotate (torque-to-turn / spin-out). Your planned assembly torque for the joint should be comfortably below that value and below the insert’s published max torque (manufacturer reference numbers are often provided in engineering tables). (www.bossard.com)
- If it spins, adjust and retest.
- Upgrade the body style: smooth → knurled or hex; consider keyed where paint/powder reduces friction.
- Resize the hole within the catalog tolerance band (too large encourages spin; too tight can scar coatings or hinder installation).
- Reduce assembly torque or change hardware class/lubrication to lower required torque for the same clamp load.
- Recheck grip range: if your stack is out of range, the insert may under-set (poor bulbing) or over-set (panel crush), both of which reduce torque-out.
Pro tips for repeatability
- Keep a validation log: hole Ø used, drill/reamer IDs, stroke setting, spin-out torque, chosen assembly torque, and notes on surface finish/coatings.
- For coated panels, validate before and after finishing if the sequence changes hole dimensions or friction.
- If the joint will see vibration, add a vibration/retorque check (nylon insert nuts, threadlocker, or prevailing-torque fasteners as appropriate).
FAQ (for People Also Ask)
What size hole for an M6 rivet-nut?
Most standard round-body M6 rivet-nuts target ≈ 9.0 mm holes; some series specify ≈ 8.8–8.93 mm depending on body style and tolerance. Always follow the exact part’s catalog page, as different families (round, knurled, plus-nut/slotted, hex) publish different hole diameters and tolerances.
What torque for an M6 screw into a rivet-nut?
As a practical starting point for common M6 joints: ~9.5 N·m with aluminum-body inserts and ~11 N·m with steel/stainless-body inserts when using class 8.8 or A2-70 hardware in dry conditions. Treat these as baseline references—adjust for lubrication, coatings, and your actual clamp-load requirement, and always validate on scrap that matches your stack.
Why did my rivet-nut spin?
Typical causes include an oversize or out-of-round hole, wrong body style for the parent material (e.g., smooth round in soft aluminum), under-set installation (insufficient stroke), or an out-of-range grip relative to your stack thickness. Remedies include switching to knurled/hex/keyed bodies, drilling to the correct catalog hole Ø, recalibrating tool stroke, and confirming you’re within the insert’s grip range.
Conclusion & CTA
Getting hole size and assembly torque right on an M6 rivet-nut dramatically reduces spin-outs, pull-throughs, and field failures. Use the tables above to pick the correct hole diameter, match the body style to your parent material and coating, and validate on scrap to confirm your torque is comfortably below spin-out and max-torque thresholds. A few minutes of validation saves hours of rework later.
CTA: Want the printable M6 Drill/Torque Cheat Sheet (A4/Letter) and a grip-range worksheet? Say the word and I’ll generate both and add them as downloadable PDFs for your post.
Sources (selected)
- Bossard/Tubtara® technical information—recommended M6 tightening torques, torque-to-turn & mechanical property examples. (www.bossard.com)
- Böllhoff RIVNUT® engineering data—torque relationships & performance notes.
- Böllhoff RIVKLE® catalog—example hole sizes (M6 Plus-Nut), dimensional conventions. (RS Components)
- NAS standards context for aerospace rivet-nuts (NAS 1329/1330).