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Description
FINISHED THREADM8 × 1
VARIANT1.5×D (12 mm)
MATERIALStainless steel
SYSTEMV-Coil
M8x1 1.5xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M8x1 1.5×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M8 × 1 |
| Thread pitch P | 1 mm |
| Length variant | 1.5×D |
| Insert height | 12 mm |
| Repair system | V-Coil |
| Compatible tap | M8x1 4H V-Coil |
| Pre-drilled hole | Ø8.3 mm |
The V-Coil M8x1 thread repair insert is a Helicoil-type stainless steel wire coil installed in a hole tapped with a thread repair tap. It restores a fully functional M8x1 thread for a standard screw, without a larger screw or part replacement. The 1.5xD variant is 12 mm high and is suitable for shallow holes and harder materials. It complies with DIN 8140, form A (free-running).
M8x1 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
1Prepare the hole
diameter: Ø8.3 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 1.5×D
✓Restore the joint
thread: M8 × 1
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 wire has a diamond-shaped cross section, so it works on both sides simultaneously: the outer edge engages the thread in the hole, while the inner edge forms a new thread for the screw. Before installation, the coil is slightly larger than the hole. As it is screwed in, the coils compress; when the tool is released, they expand and lock permanently in place — without adhesive. The wire has a minimum tensile strength of 1400 MPa — the new thread is harder and smoother than a thread cut directly into the material.
Why an STI tap is required instead of a standard M8x1 tap
The wire thickness is determined by the thread pitch: 0.65 × 1 mm ≈ 0.65 mm.
The thread for the insert is enlarged to accommodate the wire on both sides of the profile — its diameter is approx. 9.3 mm compared with 8 mm for a standard M8x1 thread.
It can only be cut with a thread repair tap M8x1 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.
M8x1 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 1.5xD version
The insert restores an M8x1 thread equally well in steel, stainless steel, cast iron and aluminum because the stainless steel coil forms the load-bearing profile, rather than the hole wall. The length is selected according to the material and screw property class. The variant 1.5xD is suitable for steel, cast iron and shallow holes. Longer 2xD and 2.5xD inserts are selected for soft metals and screws of property class 8.8 or higher. Applications include repairing banjo bolt threads in brake lines connected to motorcycle master cylinders. The first thread turn in this type of joint carries approximately half the axial load, 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.
M8x1 1.5×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M8x1 with a pitch of 1 mm.
✓Tap: special M8x1 4H V-Coil thread repair tap.
✓Tap drill hole: Ø8.3 mm drill bit.
▲Depth: space for an insert 12 mm high and proper seating.
▲
Application limitations
The thread for the insert must be cut with an M8x1 4H V-Coil STI tap — the nominal M8x1 thread is too small for the insert to anchor in it. The free-running version does not prevent the screw from loosening: threadlocker or a screw-locking insert helps under vibration.
The V-Coil M8x1 1.5xD thread repair insert creates a joint in which the screw is the weakest point, rather than the thread in the repaired part. Allow for the depth: 12 mm equals one and a half thread diameters (1.5 × 8 mm) — the hole must provide this much space. 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. The 1.5xD variant is suitable for steel, cast iron and shallow holes, 2xD is standard for aluminum, and 2.5xD works well in soft metals and with screws of property class 8.8 or higher. This insert has a length of 1.5xD (12 mm).
No — the coil is larger than the thread in the hole and locks itself permanently in place. Threadlocker is used only under severe vibration. An alternative is a screw-locking insert in accordance with DIN 8140 form B.
No — the insert requires an STI thread approximately 9.3 mm in diameter, while a standard M8x1 thread is only 8 mm, making it approximately 1.3 mm too small. Drill the hole to Ø8.3 mm and tap it with an M8x1 4H V-Coil tap.
Yes, with one proviso — the insert only restores the mechanical M8x1 thread in the hole. Banjo connections and bleeder screws are sealed by the seating surface or washer, not by the thread itself. After repair, inspect the seating surfaces and install new washers.
Product accessories
Thread repair insert M8x1 2.5xD V-Coil
Reference: 0000006044 In stock > 10 items
€0.53
€0.65 brutto
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Shipping
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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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