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Description
FINISHED THREADM7 × 1
VARIANT3×D (21 mm)
MATERIALStainless steel
SYSTEMV-Coil
M7 3xD thread repair insert – V-Coil DIN 8140 helical thread insert
Thread insert technical data table
| V-COIL M7 3×D THREAD REPAIR INSERT | |
|---|---|
| Restored thread | M7 × 1 |
| Thread pitch P | 1 mm |
| Length variant | 3×D |
| Insert height | 21 mm |
| Repair system | V-Coil |
| Compatible tap | M7 4H V-Coil |
| Pre-drilled hole | Ø7.2 mm |
The M7x1 V-Coil thread repair insert is a coil made of Helicoil-type stainless steel wire that restores a damaged thread in a hole. Once installed in a hole tapped with a thread repair tap, it creates a fully functional M7 thread for a standard bolt. This solution eliminates the need for a larger bolt and replacement of the damaged part. The 3xD version, 21 mm high, is selected for soft materials and bolts of a higher property class. The design conforms to DIN 8140, form A, which is a free-running insert.
M7 thread repair step by step – from the hole to the completed joint
Four installation steps in the V-Coil system
Thread repair process M7 × 1
1Prepare the hole
diameter: Ø7.2 mm
2Tap the thread
tool: V-Coil 4H
3Screw in the insert
length: 3×D
✓Restore the joint
thread: M7 × 1
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 needed instead of a standard M7 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. 8.3 mm compared with 7 mm for a standard M7 thread.
It can only be cut with a thread repair tap M7 4H V-Coil in a hole drilled to Ø7.2 mm; after the insert is installed, the hole returns to the nominal thread M7 × 1.
M7 thread repair in steel, stainless steel, cast iron and aluminum
When to choose the 3xD version
The insert restores threads in steel, stainless steel, cast iron, and aluminum, so one tool covers different parent materials. Select the length according to the operating conditions. The 3xD version is suitable for soft materials and bolts of property class 8.8 and higher. Choose a shorter insert for a shallow hole in steel, and a longer one when the material is soft and the load is high. Among other applications, it repairs a stripped bleeder screw thread in an aluminum brake caliper body without replacing the entire part. Distributing the load across the threads reduces the peak on the first thread from 50% to approximately 30%, 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.
M7 3×D insert compatibility – required V-Coil system tools
Check before purchasing
✓Nominal thread: M7 with a pitch of 1 mm.
✓Tap: special M7 4H V-Coil thread repair tap.
✓Tap drill hole: Ø7.2 mm drill bit.
▲Depth: space for an insert 21 mm high and proper seating.
▲
What to remember before repair
The insert requires an STI thread cut with a V-Coil system thread repair tap — a standard M7 tap cuts a smaller thread in which the insert cannot be seated. The free-running version does not lock the bolt: for joints exposed to vibration, use threadlocker or a screw-locking insert.
The M7 3xD 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: 21 mm equals three thread diameters (3 × 7 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 bolt property class: the weaker the material and the stronger the bolt, 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 for soft materials and bolts of property class 8.8+. This insert has a length of 3xD, equivalent to 21 mm.
The top coil should sit 1/4–1/2 of a turn below the material surface. After installation, break off the installation tang with a punch. In a blind hole, remove the broken fragment before installing the screw.
Yes. Insert dimensions are specified by the standard DIN 8140 and ASME B18.29.1, so products from Helicoil, V-Coil, Recoil, and BaerCoil remain interchangeable. Matching size, pitch, and length are what matter.
The insert restores the mechanical M7 thread in the hole but does not seal the joint itself. Banjo fittings and bleed screws are sealed by a sealing face or washer. After repair, inspect the sealing face and replace the washers with new ones.
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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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