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Description
FINISHED THREADM12 × 1.25
VARIANT2×D (24 mm)
MATERIALStainless steel
SYSTEMV-Coil
M12x1.25 2xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M12x1.25 2×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M12 × 1.25 |
| Thread pitch P | 1.25 mm |
| Length variant | 2×D |
| Insert height | 24 mm |
| Repair system | V-Coil |
| Compatible tap | M12x1.25 4H V-Coil |
| Pre-drilled hole | Ø12.3 mm |
The V-Coil M12x1.25 thread repair insert is a resilient Helicoil-type stainless steel wire coil. Installed in a hole tapped with a thread repair tap, it restores a fully functional M12x1.25 thread for a standard screw. It requires neither a larger screw nor replacement of the damaged part. The 2xD version with a height of 24 mm is selected for standard joints in aluminum. The design complies with DIN 8140 form A, the free-running version.
M12x1.25 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M12 × 1.25
1Prepare the hole
diameter: Ø12.3 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 2×D
✓Restore the joint
thread: M12 × 1.25
Screw in the insert using an installation tool — do not stretch it or twist it sideways.
Practical installation checks
Before installation, clean chips and coolant residue out of the hole. Screw in the insert with an installation tool, keeping it straight and using no force. A properly seated insert sits 1/4–1/2 of a turn below the surface. Finally, break off the tang (the crosspiece at the bottom of the insert) with a punch; if the hole is blind, remove the broken piece so that it does not obstruct the screw.
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 required instead of a standard M12x1.25 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. 13.62 mm compared with 12 mm for a standard M12x1.25 thread.
It can only be cut with a thread repair tap M12x1.25 4H V-Coil in a hole drilled to Ø12.3 mm; after the insert is installed, the hole returns to the nominal thread M12 × 1.25.
M12x1.25 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 2xD version
The same insert restores threads in steel, stainless steel, cast iron, and aluminum. Length selection depends on the parent material and screw property class. The 2xD version is standard for aluminum and typical loads. A shorter insert is selected for a shallow hole in steel. A longer insert is used in soft material and with screws of property class 8.8 and higher. Applications include repairing spark plug holes in the aluminum cylinder heads of newer, smaller engines. In a thread cut directly into the material, the first turn carries approximately 50% of the force, while the insert distributes it evenly — as shown in the table below.
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.
M12x1.25 2×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M12x1.25 with a pitch of 1.25 mm.
✓Tap: special M12x1.25 4H V-Coil thread repair tap.
✓Tap drill hole: Ø12.3 mm drill bit.
▲Depth: space for an insert 24 mm high and proper seating.
▲
V-Coil system requirements
Installing the insert requires an STI thread — it can only be cut with an M12x1.25 4H V-Coil thread repair tap. The free-running insert allows the screw to be screwed in and out freely; where severe vibration occurs, add threadlocker or choose a screw-locking version.
The M12x1.25 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: 24 mm equals two thread diameters (2 × 12 mm) — this is the space the hole must provide. The same insert is also used to reinforce threads in series production.
Frequently asked questions
Select the length according to the parent material and screw property class — the weaker the material and the stronger the screw, the longer the insert. The 1.5xD version is suitable for steel, cast iron, and shallow holes; 2xD is standard for aluminum, while 2.5–3xD is suitable for soft materials and screws of property class 8.8 and higher. This insert has a height of 24 mm in the 2×D version.
The top coil of the insert should sit 1/4 to 1/2 of a turn below the surface of the hole. After installation, the installation tang is broken off with a punch. In a blind hole, the broken fragment must be removed.
No, the insert requires an STI thread with a diameter of approximately 13.62 mm. A standard M12x1.25 thread measures 12 mm, making it approximately 1.6 mm too small. The hole is drilled to Ø12.3 mm and tapped with an M12x1.25 4H V-Coil tap.
Aluminum has low shear strength, and in a thread cut directly into the material, the first turn carries approximately 50% of the force. The spark plug is often removed at every service, frequently while the engine is hot. The insert distributes the load evenly across successive thread turns.
Product accessories
Thread repair tap M12x1.25 4H V-Coil
Reference: 0000005936 In stock > 10 items
€16.92
€20.81 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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