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Description
FINISHED THREADM4 × 0.7
TOLERANCE4H
PRE-DRILLED HOLEØ4.1 mm
LENGTH L158 mm
M4 thread repair tap – STI tap for V-Coil M4x0.7 inserts
Tool dimension table and technical data
| V-COIL M4 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M4 × 0.7 |
| Tolerance class | 4H |
| Tap diameter B | 4.9 mm |
| Overall length L1 | 58 mm |
| Flute length L2 | 16 mm |
| Shank diameter D2 | 5 mm |
| Square drive a | 4 mm |
| Pre-drilled hole | Ø4.1 mm |
The V-Coil M4 thread repair tap cuts an STI (Screw Thread Insert) thread for a steel Helicoil-type insert. The tool restores a load-bearing threaded hole without increasing the screw size. Once the insert is installed, the hole accepts a standard M4 screw without modifying the fastener. The 5 mm shank with a 4 mm square drive fits standard hand tap wrenches.
Repairing a stripped M4 thread in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in all of these materials: steel, stainless steel, cast iron, and aluminum. Threads strip most often in soft metals, while in steel the insert improves the fatigue life of the joint. The M4 size is found, for example, in terminals and terminal blocks for electrical equipment, as well as equipment housings. The hole diameter for the STI tap is Ø4.1 mm. Drill at the upper tolerance limit and cut the thread with coolant for a clean profile.
The M4 thread repair tap cuts an STI thread with dimensions conforming to DIN 8140-2. The tool's overall length L1 is 58 mm, and its flute length L2 is 16 mm. The tool is compatible with V-Coil inserts in lengths of 2xD, 3xD, and a correctly repaired thread carries loads comparable to or greater than the original thread.
M4 thread repair step by step
From drilling to the nominal thread
Repairing the thread is faster and less expensive than replacing the entire component, such as an electrical equipment terminal block with a damaged threaded hole.
Thread repair M4 with a wire insert
1Drilling
Hole: Ø4.1 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M4 × 0.7
In a blind hole, remove the broken-off tang before installing the screw
Helicoil M4 tap (STI) – why it is larger than a standard tap
Compensating for the wire thickness of the thread insert
The STI thread profile remains a metric 60° triangle with a 0.7 mm pitch — only the size changes. The diameter increases by twice the insert wire thickness: D STI = 4 + 1.3 × 0.7 = 4.91 mm. This is why the tool's cutting section measures 4.9 mm, and neither an M5 nor an M6 tap can replace it. Class 4H is the metric equivalent of inch class 3B, also recommended for screw-locking inserts. Once the insert is installed, the bolt engages a standard class 6H thread.
Tap compatibility with the V-Coil insert
What must match before starting the repair
✓Matching size: V-Coil M4 insert with a 0.7 mm pitch.
✓Matching hole: prepare a Ø4.1 mm diameter before tapping.
✓Matching version: available M4 insert lengths: 2xD, 3xD.
▲Required inspection: depth and wall thickness of the component being repaired.
Tool exclusively for insert threads
The thread cut by this tool is larger than nominal and is intended exclusively for installing a V-Coil insert. Use a standard tap to cut a regular M4 thread — never use it to cut the seat for an insert.
Frequently asked questions
For the STI thread, use a drill bit Ø4.1 mm, rather than 3.3 mm as for a standard M4 thread. Drill near the upper tolerance limit and chamfer the hole entrance at 90–120°.
No, the STI thread has a nonstandard diameter 4.91 mm, which neither M5 nor M6 can reproduce. An incorrect profile prevents the insert from locking properly. The tool's cutting diameter B is 4.9 mm.
Yes, the inner edge of the wire recreates the nominal thread M4 × 0.7. The minor diameter after installation is approximately 3.24 mm, in accordance with ISO 724. A standard screw fits without any modifications.
Yes, the free-running insert 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 joint each time it is tightened.
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| 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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