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Description
FINISHED THREADM8 × 1.25
VARIANT3×D (24 mm)
MATERIALStainless steel
SYSTEMV-Coil
M8 3xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M8 3×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M8 × 1.25 |
| Thread pitch P | 1.25 mm |
| Length variant | 3×D |
| Insert height | 24 mm |
| Repair system | V-Coil |
| Compatible tap | M8 4H V-Coil |
| Pre-drilled hole | Ø8.3 mm |
The M8x1.25 V-Coil thread repair insert made of Helicoil-type stainless steel wire restores a stripped thread in a metal housing. Installed in a hole tapped with a thread repair tap, it creates a fully functional M8 thread for a standard bolt. The repair does not require a larger bolt or replacement of the entire part. The 3xD version, 24 mm high, is selected for soft materials and heavily loaded joints. The insert conforms to DIN 8140, form A, which is the free-running version.
M8 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M8 × 1.25
1Prepare the hole
diameter: Ø8.3 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 3×D
✓Restore the joint
thread: M8 × 1.25
Screw in the insert using an installation tool — do not stretch it or twist it sideways.
Practical installation checks
A clean hole is essential for straightforward installation — remove chips and coolant residue. Install the insert with an installation tool, without forcing or tilting it. The top coil should sit 1/4–1/2 of a turn below the material surface. Break off the tang with a punch; always 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 wire has a diamond-shaped cross section: one edge acts as a screw in relation to the hole, and the other as a nut in relation to the screw being installed. The free coil is slightly larger than the thread in the hole; as it is screwed in, it contracts elastically, then expands upon release and locks permanently in place without adhesive or additional components. Cold-rolled wire with a minimum tensile strength of 1400 MPa produces a thread that is harder and smoother than one cut directly into the material.
Why an STI tap is needed instead of a standard M8 tap
The wire thickness is determined by the thread pitch: 0.65 × 1.25 mm ≈ 0.81 mm.
The thread for the insert is enlarged to accommodate the wire on both sides of the profile — its diameter is approx. 9.62 mm compared with 8 mm for a standard M8 thread.
It can only be cut with a thread repair tap M8 4H V-Coil in a hole drilled to Ø8.3 mm; after the insert is installed, the hole returns to the nominal thread M8 × 1.25.
M8 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 3xD version
The insert restores threads in steel, stainless steel, cast iron, and aluminum, so one solution covers different housings. The length is selected according to the parent material and bolt property class. The 3xD version is suitable for soft alloys and bolts of property class 8.8 and higher. A shorter insert is selected for shallow holes and hard steel. Repairs include stripped accessory mounting threads in an aluminum engine block. The insert evens out the load on the threads, since the first thread of a standard tapped hole carries approximately half the force.
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.
M8 3×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M8 with a pitch of 1.25 mm.
✓Tap: special M8 4H V-Coil thread repair tap.
✓Tap drill hole: Ø8.3 mm drill bit.
▲Depth: space for an insert 24 mm high and proper seating.
▲
Application limitations
The thread for the insert must be cut with an M8 4H V-Coil STI tap — a nominal M8 thread is too small for the insert to anchor in it. The free-running version does not prevent the bolt from loosening: threadlocker or a screw-locking insert helps under vibration.
A correctly installed M8 3xD V-Coil thread repair insert transfers loads so that the bolt shank fails before the thread in the material. Plan the hole depth: the insert occupies 24 mm, or three thread diameters (3 × 8 mm). In series production, the same insert serves as preventive reinforcement.
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. For steel, cast iron, and shallow holes, 1.5xD is sufficient, while 2xD is standard for aluminum. This insert has a length of 3xD (24 mm), intended for soft materials and bolts of property class 8.8 and higher.
No, the coil is larger than the tapped hole thread and wedges permanently into it. Threadlocker is used only under severe vibration. An alternative is a screw-locking insert conforming to DIN 8140, form B.
No, the insert requires an STI thread with a diameter of approximately 9.62 mm. A standard M8 thread is 8 mm, making it approximately 1.6 mm too small. The hole is drilled to Ø8.3 mm and tapped with an M8 4H V-Coil tap.
Yes, the same inserts are installed at the factory to reinforce threads in cast iron and aluminum. The thread gains the hardness of wire with a minimum tensile strength of 1400 MPa and an even load distribution. This design also improves the fatigue life of the joint.
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All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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