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Description
FINISHED THREADM8 × 1.25
VARIANT2×D (16 mm)
MATERIALStainless steel
SYSTEMV-Coil
M8 2xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M8 2×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M8 × 1.25 |
| Thread pitch P | 1.25 mm |
| Length variant | 2×D |
| Insert height | 16 mm |
| Repair system | V-Coil |
| Compatible tap | M8 4H V-Coil |
| Pre-drilled hole | Ø8.3 mm |
The V-Coil M8x1.25 thread repair insert is a Helicoil-type stainless steel wire coil that restores a damaged internal thread. Installed in a hole tapped with a thread repair tap, it creates a fully functional M8 thread for a standard screw. There is no need for a larger screw or replacement of the part. The 2xD version with a height of 16 mm is a standard solution for holes of average depth. The design complies with the standard DIN 8140 in form A, i.e., free-running.
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: 2×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 a standard M8 tap cannot prepare the insert hole
A pitch of 1.25 mm means a wire thickness of approx. 0.81 mm (the 0.65 × P rule).
The installation thread for the insert is therefore approx. 9.62 mm in diameter — approx. 1.6 mm larger than the nominal 8 mm of an M8 thread.
It can only be prepared with a tap M8 4H V-Coil after drilling Ø8.3 mm; after repair, the screw engages a standard thread M8 × 1.25.
M8 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 2xD version
The insert restores threads equally well in steel, stainless steel, cast iron, and aluminum, as well as magnesium and plastics. The parent material and screw property class determine the length. The version 2xD is suitable for general use. A shorter insert is selected for a shallow hole in steel, and a longer one for soft material and screws of property class 8.8 or higher. Repairs include stripped accessory mounting threads in an aluminum housing. Distributing pressure across the thread turns is essential here, since the first turn of a standard thread 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 2×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 16 mm high and proper seating.
▲
V-Coil system requirements
Installing the insert requires an STI thread, which can only be cut with an M8 4H V-Coil thread repair tap. The free-running insert allows the screw to be installed and removed freely; where severe vibration occurs, add threadlocker or select a screw-locking version.
The M8 2xD V-Coil thread repair insert creates a joint in which the weakest point is the bolt, rather than the thread in the repaired part. Allow for the depth: 16 mm equals two thread diameters (2 × 8 mm) — this is the space the hole must provide. The same insert is also used to reinforce threads in series production.
Frequently asked questions
The parent material and screw property class determine the length. The 1.5xD version is sufficient for steel, cast iron, and shallow holes; 2xD is standard for aluminum, while 2.5–3xD is used in soft alloys and with screws of property class 8.8 or higher. The insert shown has a length of 2×D (16 mm).
The top turn of the insert should sit 1/4 to 1/2 of a turn below the surface around the hole. After installation, break off the installation tang with a punch. In a blind hole, the broken fragment must be removed before installing the screw.
No, the insert requires an STI thread with a diameter of approximately 9.62 mm. A standard M8 thread is 8 mm in diameter, making it approximately 1.6 mm too small. Drill the hole to Ø8.3 mm and tap it with the tap M8 4H V-Coil.
Yes, the same inserts are factory-installed to reinforce threads in cast iron and aluminum. The thread gains the hardness of the wire with a minimum tensile strength of 1400 MPa and an even load distribution. This also improves the fatigue life of the joint.
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| 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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