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Threaded Inserts — Complete Guide

A complete engineering guide to threaded inserts: Helicoil/STI wire inserts, Keensert, Time-Sert, rivet nuts, PEM self-clinching inserts, plastic inserts (ultrasonic, heat-set), Rosan aerospace inserts, E-Z Lok, a comparison table, and interactive drill-size calculators.

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Rigid — Threaded Inserts
Helicoil · Keensert · Time-Sert · Rivet Nut · Press-fit · Plastic · Rosan · E-Z Lok · Comparison · Calculators
🌀 Helicoil / Wire Thread Insert — STI
What is a Helicoil?
Most CommonNASM 21209
PrincipleA coiled stainless steel wire inserted into an STI hole → a new thread
StrengthStronger than the original thread in Al! ×1.5-2 pull-out
Insert MaterialSS 304 · SS 316 · Phosphor Bronze · Inconel 600
SizesM3 to M39 · UNC 4-40 to 3/4"-10
Depth1D · 1.5D (common) · 2D · 2.5D · 3D
StandardsNASM 21209 · MIL-I-8846 · DIN 8140 · BS 4255
UsesThread repair · Al/Mg → ↑strength · engines · aerospace
▶ YouTube
STI Tap Drill — Helicoil Drills
Larger than standard!
⚠️ ImportantSTI Tap = larger than Standard! Use the table only
SizePitchSTI DrillStandard Drill
M30.53.6mm2.5mm
M40.74.7mm3.3mm
M50.85.9mm4.2mm
M61.07.0mm5.0mm
M81.259.2mm6.8mm
M101.511.3mm8.5mm
M121.7513.5mm10.2mm
M162.017.7mm14.0mm
Installation Process
5 Steps
1. DrillSTI Tap Drill — per table
2. STI TapHelicoil tap (not standard!)
3. InsertionInsertion tool ← threads in ← insert
4. Break TangNotch (Tanged) → break the tang ← inside the tool
5. TanglessNo tang — no breaking needed! (aerospace)
Minimum depth: 1.5D · Recommended: 2D for high loads
▶ YouTube
Tangless Helicoil
NASM 21209-3TAerospace
AdvantageNo tang to break → ↓time · ↓risk
InsertionSpecial insertion tool ← ←
RemovalRemovable ← special extraction tool
StandardNASM 21209-3T · AS1085 (USAF)
UseAerospace · hard-to-reach areas · clean room
▶ YouTube
Recoil — Equivalent to Helicoil
AustraliaSTI Compatible
ManufacturerRecoil — Australia · Snap-on Industrial
CompatibilityCompatible with Helicoil ← the same STI taps!
Advantage↓price vs. Helicoil · Tangless available
MaterialsSS 304 · SS 316 · Phosphor Bronze
Manufacturer: recoil.com.au
Helicoil Applications
When to Use
Thread RepairA stripped/seized thread → Helicoil = like new
Al/Mg → SteelA steel bolt in Al → Helicoil protects!
Engine HeadsClean ← tap ← insert ← back to service
Lathe BodyHelicoil in cast iron ← ↑pull-out
Not RecommendedVery high pressures — Keensert is preferable
🔐 Keensert / Key-Lock Insert — Solid Rigid
What is a Keensert?
Solid!NASM 33537
PrincipleA solid stainless steel insert with locking keys
Locking4 keys bite into the parent material → never rotates
Strength↑↑ Pull-out vs. Helicoil — recommended for heavy loads
MaterialSS 303 · SS 316 · Inconel 718
SizesM6 to M39 · #10-32 to 1"-8
StandardsNASM 33537 · MS122073 · DIN 8140 Type D
UseAerospace · defense · heavy loads · repeated-use Al
▶ YouTube
Keensert Drill Chart
Special drill!
SizePitchDrillMin Depth
M61.08.0mm9.0mm
M81.2510.5mm12.0mm
M101.512.5mm15.0mm
M121.7515.0mm18.0mm
M162.020.0mm24.0mm
M202.525.0mm30.0mm
⚠️ Mandatory to use a Keensert Tap (different from standard!)
Keensert Installation Process
4 Steps
1. DrillKeensert Drill Size
2. TapKeensert Tap (not STI, not Standard!)
3. InsertionSpecial insertion driver ← bolt inserted
4. Key LockA locking tool strikes the keys inward → locks!
⚠️ Cannot be removed after key locking — permanent!
▶ YouTube
Keensert vs Helicoil
Comparison
Pull-out StrengthKeensert ↑↑ vs. Helicoil
Size RepairBoth — Helicoil easier
RemovalHelicoil ✅ · Keensert ❌ (permanent)
PriceKeensert more expensive
Heavy LoadKeensert preferable
Quick RepairHelicoil preferable
🔧 Time-Sert / Solid Thread Repair
Time-Sert — a Solid Insert with a Flange
Engine head repair
PrincipleA solid insert + flange → locks at the top
LockingThe flange expands on installation → mechanical lock
StrengthVery high — the flange carries shear load
MaterialMild Steel (FineTech) · SS 303
Main UseEngine head bolts (M8/M10/M11/M12) · Al wheel taps
AdvantageNo special Helicoil Tap needed — Standard Tap!
Manufacturers: Time-Sert · Böllhoff TRISERT
▶ YouTube
ENSAT — Böllhoff Solid Insert
DIN 16903Common in Europe
TypesType 140 (Hex Drive) · Type 302 (Slot Drive) · Type 160
DIN 16903European ENSAT standard
PrincipleA larger external thread + standard internal · locks by threading
MaterialsSteel · SS 303 · Brass
UseRepair · Al/Zn die casting · rigid plastic
ToolStandard Tap + Hex insertion driver
▶ YouTube
Locking vs Non-Locking
Selection
Non-LockingRemovable · repair only
LockingLocks the flange · permanent · high loads
When Locking?Engine heads · dynamic loads · vibration
Prevailing TorqueThe insert deforms slightly → counter-rotation force
🔴 Rivet Nut / Blind Nut / Nutsert
Rivet Nut — Principle
One-sided accessPEM · Avdel
PrincipleInserted into a hole → pulled → expands → locks
AdvantageOne-sided access only! ← like a Pop Rivet
MaterialAl · SS · Mild Steel · Cu-Ni · Monel
SizesM3 to M16 · #6-32 to 1/2"-13
Material Thickness0.5-6mm depending on size
UsesElectrical equipment · automotive · enclosures · sheet metal
▶ YouTube
Rivet Nut Types
4 Main Types
Round BodyMost common · rotates in a round hole · up to 15kN
Hex Body↑strength · doesn't rotate! · for vibration
Flat HeadFlat head · doesn't protrude
Countersunk (CSK)Sinks into the surface → aerodynamic
Large FlangeSoft/thin material → ↑grip
SealedA sealed back → sealing · marine · outdoor
▶ YouTube
Rivet Nut — Hole Sizes
Hole Size
SizeDrill (Round)Drill (Hex)Max Thickness
M35.4mm—2.0mm
M46.4mm6.4mm3.0mm
M57.7mm7.8mm3.5mm
M69.0mm9.0mm4.0mm
M811.5mm11.5mm5.0mm
M1014.0mm14.0mm6.0mm
Installation Tools
Hand · Pneumatic · Electric
Hand ToolFrom M3 to M10 · for small quantities
Pneumatic↑speed · from M3 to M16
Cordless (Avdel)Mobility · consistent · M4-M12
Press (Auto)Production line: precise force
Check Pull Force per item! ← tightening intensity is critical
▶ YouTube
⚙️ Press-fit / Self-Clinching Inserts — PEM
Self-Clinching Standoff / Nut
PEMThin metal sheets
PrinciplePress ← ← insert seats ← material flows around it
ResultA permanent joint ← high push-out force
Minimum Thickness0.5-1.5mm (depending on size and material)
Sheet MaterialsAl (Hard) · Steel · SS · Copper
⚠️ Soft AlSoft Al (1xxx) ← not suitable! PEM falls out
UsesPCB · signage · electrical cabinets · electronics
Manufacturer: PEM (Parker Hannifin)
▶ YouTube
Main PEM Types
S · SS · SO · SOFS
S (Nut)Press-in nut · M2 to M10 · steel
SS (Nut SS)Stainless · M2-M10
SO (Standoff)Spacer + thread · M2-M8 · adds height
SOFS (Floating)Thread floats ± 0.5mm · ← compensates for misalignment
K (Stud)Fixed stud · M2-M8
FH (Flush Head)Flush head · aerodynamic
Installing PEM
Press + Anvil
ToolA press (Hand/Pneumatic/C-Press) + a matching anvil
Installation Force0.3-35kN depending on size (from PEM chart)
⚠️ AnvilMandatory! Without an anvil = a bent sheet
TestingPush-out Force Test · Torque Test per PEM Spec
Never with a hammer! Press only
▶ YouTube
Spirol / HAEGER Alternatives
PEM Equivalents
SpirolCoiled Pins + Inserts · self-clinching
HAEGERA machine manufacturer + unique insert
Böllhoff RIVKLEBlind Rivet Element
Captive NutA retained nut ← held within a frame
🔵 Inserts for Plastic — Plastic Threaded Inserts
Ultrasonic Insert
Thermoplastic↑strength
Principle20-40kHz vibration ← local heat ← the plastic melts around the insert
Insert MaterialBrass H59 usually · SS · Al
Suitable PlasticsPA · ABS · PC · POM · PBT · PEEK
Advantage↑↑ pull-out strength · fast · clean
⚠️ Not forThermoset (Epoxy/Phenol) — doesn't melt!
UsesConsumer products · medical · electronic equipment
Manufacturers: Böllhoff AMTEC · Accu · PEM Plastic
▶ YouTube
Heat-Set Insert
Heat3D Print
PrincipleHeat (soldering iron/oven) ← the insert sinks into soft plastic
Installation Temp.150-300°C depending on plastic
PLA150-180°C
ABS / PETG200-240°C
⭐ 3D PrintA 3D printer → Heat-Set Inserts = the common solution!
ToolSoldering iron + special tip · Weller · Hakko
▶ YouTube
Press-in Insert — Cold Press
Simple↓strength
PrinciplePress ← ← a tight fit
StrengthRelatively low — ↓pull-out
Knurled BodyA grooved body → ↑grip
UseRigid plastic · low loads
Not SuitableDynamic loads · vibration
▶ YouTube
Expansion Insert
Thermoset · Composites
PrincipleA tightened bolt → the insert body expands
UseThermoset plastics · composites · rigid plastic
AdvantageNo heat — suitable for Thermoset!
StrengthMedium · depends on host material
Manufacturer: Spirol · KVT
▶ YouTube
Molded-in Insert
Strongest
PrincipleThe insert sits in the mold ← molded around it
Strength↑↑↑ Highest — part of the part's structure
⚠️ DrawbackComplicates tooling · the insert must be held in place
UseCritical molded products · medical · aerospace
✈️ Rosan / Aviation Inserts
Rosan Insert — What Is It?
NAS1130Aerospace Only
PrincipleA solid insert with a Locking Ring → locks after insertion
Locking RingAn Al/Ti ring is pressed ← ← the insert fully locks
Strength↑↑↑ Pull-out — aerospace certified
MaterialsTi · SS A286 · Inconel · Al 7075
StandardsNAS1130 · MS21209 · AS4536
UseAircraft frame · structural Al/Ti · critical joints
Manufacturers: Rosan Inc. · LISI Aerospace · Aviall
▶ YouTube
Rosan Types
A · B · C · D
Type AStandard — regular wall
Type B (Thin)Thin wall — ↑strength
Type C (Nut)With a hex nut for counter-rotation
Type D (Double)A double seat — high loads
SealedWith a seal — pressure/fluid environments
Spiralock — Aviation Locking
MIL-DTL-18240
PrincipleInternal thread with a wide 30° wedge ramp ← locks
Not NeededNyloc / Loctite / Safety Wire — ← Spiralock alone
Self-LockVibration → the bolt doesn't loosen! ← guaranteed
UseAerospace · defense · space · rocket engines
Manufacturer: Spiralock (Stanley)
▶ YouTube
🟢 E-Z Lok — Inserts for Soft Materials
E-Z Lok — Principle
Al · Wood · Plastic
PrincipleAn insert with a coarse external thread → screwed in by rotation
ExternalCoarse thread/knurl → grip in soft material
InternalA standard M thread
MaterialsBrass · SS · Al · Zinc
Host MaterialsWood · plastic · soft Al · MDF · foam
UseFurniture · models · enclosures · prototyping
Manufacturer: E-Z Lok · Rockler (wood)
▶ YouTube
E-Z Lok Types
By host material
Through-ThreadExternal thread ← hand-turned
Flush Press-InPress + knurl · ← plastic
Knife ThreadSharp teeth → self-cutting · wood
Wood InsertBarrel Nut / Tee Nut for furniture
LockingInternal Nyloc ← ↓vibration loosening
Tee Nut / Barrel Nut — Furniture
Wood / MDF
Tee NutA flange + teeth → hammered in ← ←
Barrel NutCylindrical ← inserted · ← knock-down furniture
Cross DowelReplaces a Barrel Nut · ↑strength
SizesM4 · M5 · M6 · M8 — the common ones
▶ YouTube
📊 Comparison Table — All Rigid Insert Types
TypePrinciplePull-out StrengthPermanent/RemovableAccessHost MaterialMain UseRelative Price
Helicoil STICoiled wire⭐⭐⭐⭐Removable ✅One-sidedAny metalRepair · Al💰💰
KeensertSolid + keys⭐⭐⭐⭐⭐Permanent ❌One-sidedAl · steelAerospace · heavy💰💰💰
Time-SertSolid + flange⭐⭐⭐⭐⭐Permanent ❌One-sidedAl · CIEngine heads💰💰💰
Rivet NutExpanding⭐⭐⭐Permanent ❌One-sided ✅Sheet · AlEnclosures · automotive💰
PEM Self-ClinchPress⭐⭐⭐⭐Permanent ❌Two-sidedSheet 0.5-3mmPCB · electronics💰💰
Ultrasonic InsertVibration⭐⭐⭐⭐Permanent ❌One-sidedThermoplasticConsumer products💰💰
Heat-Set InsertHeat⭐⭐⭐Permanent ❌One-sidedPLA/ABS/PC3D printing💰
Rosan NAS1130Locking Ring⭐⭐⭐⭐⭐Permanent ❌One-sidedStructural Al/TiAerospace💰💰💰💰
E-Z LokCoarse thread⭐⭐Removable ✅One-sidedWood · plasticFurniture · models💰
Quick Selection Guide
Key Questions
Quick thread repair→ Helicoil STI
Heavy load / defense→ Keensert
Engine head→ Time-Sert
Sheet metal / one-sided access→ Rivet Nut
Thin metal sheet (PCB)→ PEM Self-Clinching
3D-printed plastic→ Heat-Set Insert
Aerospace / certified→ Rosan / Keensert
Wood / soft material→ E-Z Lok / Tee Nut
Key Standards
Standards
NASM 21209Helicoil / Wire Thread Insert
NASM 33537Key-Lock Insert (Keensert)
NAS1130Rosan Inserts (Aviation)
DIN 8140Wire Thread Inserts (EU)
DIN 16903Solid Inserts (ENSAT)
MIL-I-8846Military Wire Insert
IFI-432Self-Clinching Fasteners (PEM)
🧮 Insert Calculators — Pre-Drill Calculator
STI Drill Calculator — Helicoil
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Rivet Nut Calculator — Hole Size
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