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Description
FINISHED THREADM14 × 1.25
VARIANT1.5×D (21 mm)
MATERIALStainless steel
SYSTEMV-Coil
M14x1.25 1.5xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M14x1.25 1.5×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M14 × 1.25 |
| Thread pitch P | 1.25 mm |
| Length variant | 1.5×D |
| Insert height | 21 mm |
| Repair system | V-Coil |
| Compatible tap | M14x1.25 4H V-Coil |
| Pre-drilled hole | Ø14.3 mm |
The V-Coil M14x1.25 thread repair insert is a Helicoil-type stainless steel wire coil that restores a stripped thread in a hole. Installed in a hole tapped with a thread repair tap, it creates a fully functional M14x1.25 thread for a standard screw. It requires neither a larger screw nor replacement of the entire part. The variant 1.5xD with a height of 21 mm is selected for shallow holes and harder materials. The dimensions are specified by DIN 8140 form A, corresponding to a free-running insert.
M14x1.25 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M14 × 1.25
1Prepare the hole
diameter: Ø14.3 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 1.5×D
✓Restore the joint
thread: M14 × 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 insert is a resilient helix made from diamond-section wire. The outer edge of the diamond anchors in the enlarged 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 upon release 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 M14x1.25 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. 15.62 mm compared with 14 mm for a standard M14x1.25 thread.
It can only be cut with a thread repair tap M14x1.25 4H V-Coil in a hole drilled to Ø14.3 mm; after the insert is installed, the hole returns to the nominal thread M14 × 1.25.
M14x1.25 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 1.5xD version
The insert restores threads in steel, stainless steel, cast iron and aluminum, making it suitable for most threaded holes. The variant 1.5xD is suitable for shallow holes and harder parent materials, where a shorter coil is sufficient to carry the load. Longer 2xD or 2.5xD inserts are selected for soft materials and screws of property class 8.8 or higher. Applications include repairing an M14x1.25 spark plug thread in an aluminum cylinder head. The coil arrangement distributes the force so that the first thread turn carries approximately half the load.
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.
M14x1.25 1.5×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M14x1.25 with a pitch of 1.25 mm.
✓Tap: special M14x1.25 4H V-Coil thread repair tap.
✓Tap drill hole: Ø14.3 mm drill bit.
▲Depth: space for an insert 21 mm high and proper seating.
▲
V-Coil system requirements
Installing the insert requires an STI thread — it can only be cut with an M14x1.25 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.
After installation of the V-Coil M14x1.25 1.5xD thread repair insert, the screw determines the joint's load limit, rather than the thread in the part. The hole must accommodate the 21 mm insert (1.5 × 14 mm) along with the proper recess below the surface. In addition to repairs, the insert is suitable for reinforcing threads during manufacturing.
Frequently asked questions
The length is determined by the parent material and screw property class: the weaker the material and the stronger the screw, the longer the insert. For steel, cast iron and shallow holes, 1.5xD is sufficient; for aluminum, 2xD is standard; and for screws of property class 8.8 or higher and soft materials, 2.5–3xD is selected. This insert is the variant 1.5xD with a height of 21 mm.
No. The coil is larger than the thread in the hole, so it locks itself permanently in place once screwed in. Threadlocker is used only under severe vibration; an alternative is a DIN 8140 form B screw-locking insert.
Yes. Insert dimensions are specified by DIN 8140 and ASME B18.29.1, so Helicoil, V-Coil, Recoil and BaerCoil products are interchangeable. The size, pitch and length must match.
Aluminum has low shear strength, and in a thread cut directly into the cylinder head, the first turn carries approximately 50% of the total load. In addition, the spark plug is removed from its threaded hole during every service, often with the engine hot. The insert distributes the load evenly across successive thread turns.
Product accessories
Thread repair tap M14x1.25 4H V-Coil
Reference: 0000006028 In stock > 10 items
€19.47
€23.95 brutto
Thread repair insert M14x1.25 2.5xD V-Coil
Reference: 0000006046 In stock > 10 items
€1.05
€1.29 brutto
Thread repair insert M14x1.25 2xD V-Coil
Reference: 0000007177 In stock > 10 items
€1.05
€1.29 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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