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Description
FINISHED THREADM9 × 1.25
VARIANT3×D (27 mm)
MATERIALStainless steel
SYSTEMV-Coil
M9x1.25 3xD thread repair insert – V-Coil helical thread insert DIN 8140
Thread insert technical data table
| V-COIL M9x1.25 3×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M9 × 1.25 |
| Thread pitch P | 1.25 mm |
| Length variant | 3×D |
| Insert height | 27 mm |
| Repair system | V-Coil |
| Compatible tap | M9x1.25 4H V-Coil |
| Pre-drilled hole | Ø9.3 mm |
M9x1.25 thread repair insert V-Coil is a Helicoil-type stainless steel wire coil. When screwed into a hole tapped with a thread repair tap, it restores a fully functional M9x1.25 thread for a standard bolt. It retains the original joint size instead of requiring the hole to be drilled out for M10. The 3xD version, with a height of 27 mm, is the longest version, for soft materials and heavily loaded joints. Dimensions are specified by DIN 8140 (form A, free-running).
M9x1.25 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M9 × 1.25
1Prepare the hole
diameter: Ø9.3 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 3×D
✓Restore the joint
thread: M9 × 1.25
Screw in the insert using an installation tool — do not stretch it or twist it sideways.
Practical installation checks
At a length of 27 mm, drilling perpendicular to the surface determines whether the bolt will screw in freely. Remove chips and coolant from the hole, and fit the insert with an installation tool without forcing it. The top coil should sit 1/4–1/2 of a turn below the material surface. Break off the tang with a punch; be sure to remove it from a blind hole.
Helicoil-type insert made from diamond-section wire – construction and operating principle
How the insert stays in the hole
The insert is a resilient helix made from diamond-section wire. The outer edge of the diamond anchors in the oversized thread in the hole, while the inner edge restores the nominal thread for the screw. In its free state, the coil is larger than the hole — installation compresses it, and once released, the coils expand and hold without adhesive. The wire has a minimum tensile strength of 1400 MPa, so the new thread is harder than the original and noticeably smoother.
Why an STI tap is required instead of a standard M9x1.25 tap
The wire thickness depends on the thread pitch: 0.65 × 1.25 mm ≈ 0.81 mm.
The thread for the insert is enlarged by the wire on both sides of the profile — its diameter is approximately 10.63 mm compared with 9 mm for a standard M9x1.25 thread.
Only a V-Coil M9x1.25 4H thread repair tap can cut it in a hole drilled to Ø9.3 mm; after the insert is installed, the hole returns to the nominal M9 × 1.25 thread.
M9x1.25 thread restoration in aluminum, cast iron, and steel
When to choose the 3xD version
The insert restores threads in steel, stainless steel, cast iron, and aluminum, as well as magnesium and plastics. The length is selected to suit the parent material and bolt property class. Choose the 3xD version where the material is soft and the bolt is strong: aluminum castings, magnesium alloys, and joints using bolts of property class 8.8 or higher. In steel and cast iron, a shorter 1.5xD insert does the same job, while 2xD is standard for aluminum under moderate loads. M9x1.25 is an uncommon size — it is found in machines and vehicles where the threaded hole was designed between the common M8 and M10 sizes. In a threaded joint, the first thread carries approximately half the force; the table below shows the load distribution.
Thread strength: how much load each turn carries
| Thread turn | Standard thread (without an insert) | Thread with a V-Coil insert |
|---|---|---|
| 1 (first from the screw head) | 50% | 30% |
| 2 | 25% | 22% |
| 3 | 12% | 17% |
| 4 | 6% | 13% |
| 5 | 3% | 10% |
| 6 | 2% | 8% |
How to read the table: when the screw is tightened, each thread turn carries part of its load. In a standard thread, the first turn carries as much as 50% of the load — and it strips first. With an insert, the same turn carries only 30% because the load is distributed over the entire thread length. Catalog data from wire thread insert manufacturers.
M9x1.25 3×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M9x1.25 with a pitch of 1.25 mm.
✓Tap: special M9x1.25 4H V-Coil thread repair tap.
✓Tap drill hole: Ø9.3 mm drill bit.
▲Depth: space for an insert 27 mm high and proper seating.
▲
Application limitations
The thread for the insert must be cut with an M9x1.25 4H V-Coil STI tap — the nominal M9x1.25 thread is too small for the insert to anchor in it. The free-running version does not prevent the screw from loosening: threadlocker or a screw-locking insert helps under vibration.
A correctly installed M9x1.25 3xD V-Coil thread repair insert carries loads so that the bolt shank fails before the thread in the parent material. Plan the hole depth: the insert occupies 27 mm, or three thread diameters (3 × 9 mm). In series production, the same insert provides preventive reinforcement of the threaded hole in the casting.
Frequently asked questions
The length depends on the parent material and bolt property class: the weaker the material and the stronger the bolt, the longer the insert required. The 1.5xD version is suitable for steel, cast iron, and shallow holes, 2xD is standard for aluminum, and 2.5–3xD is suitable for soft materials and bolts of property class 8.8 or higher. This insert is 3×D (27 mm) long.
The insert retains the original bolt size and fit with the mating component. Drilling out for M10 requires replacing the bolt and enlarging the through hole in the other part; in a thin wall, it removes material that cannot be recovered.
Yes — insert dimensions are specified by DIN 8140 and ASME B18.29.1, so Helicoil, V-Coil, Recoil, and BaerCoil models are interchangeable. Size, pitch, and length must match.
No — the coil is larger than the thread in the hole and locks itself permanently in place. Threadlocker is only needed under severe vibration; an alternative is a form B screw-locking insert in accordance with DIN 8140.
Product accessories
Thread repair tap M9x1.25 4H V-Coil
Reference: 0000005933 In stock > 10 items
€10.53
€12.95 brutto
Thread repair insert M9x1.25 2xD V-Coil
Reference: 0000007492 In stock > 10 items
€0.53
€0.65 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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