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Description
FINISHED THREADM4 × 0.7
VARIANT2×D (8 mm)
MATERIALStainless steel
SYSTEMV-Coil
M4 2xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M4 2×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M4 × 0.7 |
| Thread pitch P | 0.7 mm |
| Length variant | 2×D |
| Insert height | 8 mm |
| Repair system | V-Coil |
| Compatible tap | M4 4H V-Coil |
| Pre-drilled hole | Ø4.1 mm |
The M4x0.7 V-Coil thread repair insert made from Helicoil-type stainless steel wire restores damaged threads in metal. When installed in a hole tapped with a thread repair tap, it creates a fully functional M4 thread for a standard screw. The repair requires neither a larger screw nor replacement of the entire component. The 2xD version with a height of 8 mm is selected for holes of standard depth. The design complies with DIN 8140 form A, the free-running version.
M4 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M4 × 0.7
1Prepare the hole
diameter: Ø4.1 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 2×D
✓Restore the joint
thread: M4 × 0.7
Screw in the insert using an installation tool — do not stretch it or twist it sideways.
Practical installation checks
After tapping, remove chips and coolant from the hole. Guide the insert with an installation tool without applying pressure — it should screw in easily. The correct depth is 1/4–1/2 of a turn below the material surface. Break off the tang with a punch, and remove the broken piece 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 a standard M4 tap will not work here
The insert wire has a thickness of approx. 0.45 mm (calculated from the thread pitch: 0.65 × 0.7 mm).
The thread for the insert must accommodate the wire on both sides of the profile, so its diameter is approx. 4.91 mm — approximately 0.9 mm larger than a standard M4 thread (4 mm).
This enlarged thread can only be cut with a thread repair tap M4 4H V-Coil, after drilling the hole Ø4.1 mm. Once the insert is screwed in, the screw again engages a standard thread M4 × 0.7.
M4 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 2xD version
The insert restores threads in steel, stainless steel, cast iron, and aluminum, as well as magnesium and plastics. The 2xD version, with a height equal to twice the thread diameter, is a versatile solution. The shorter 1.5xD insert is selected for shallow holes in steel and cast iron. A longer insert is used for soft materials and screws of property class 8.8 or higher. Applications include terminals and terminal blocks in electrical equipment, where frequent tightening wears the thread. The installed insert distributes the load across all thread turns, and the first 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.
M4 2×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M4 with a pitch of 0.7 mm.
✓Tap: special M4 4H V-Coil thread repair tap.
✓Tap drill hole: Ø4.1 mm drill bit.
▲Depth: space for an insert 8 mm high and proper seating.
▲
Application limitations
The thread for the insert must be cut with an M4 4H V-Coil STI tap — a nominal M4 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.
The M4 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: 8 mm equals two thread diameters (2 × 4 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 length is selected according to 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 soft magnesium alloys and plastics with screws of property class 8.8+ require 2.5–3xD. The insert offered has a length of 2×D (8 mm).
The top turn of the insert should sit 1/4–1/2 of a turn below the material surface. After installation, the installation tang is broken off with a punch. In a blind hole, the broken fragment is removed to prevent it from obstructing the screw.
No, because the insert requires an STI thread with a diameter of approximately 4.91 mm. A standard M4 thread measures 4 mm, making it approximately 0.9 mm too small. The hole is drilled to Ø4.1 mm and tapped with an M4 4H V-Coil tap.
Yes, the free-running version is designed for repeated assembly and disassembly. The hard wire with a minimum tensile strength of 1400 MPa does not strip like a soft aluminum thread. Distributing the load across all thread turns protects the thread each time it is tightened.
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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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