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Description
FINISHED THREADM3 × 0.5
TOLERANCE4H
PRE-DRILLED HOLEØ3.1 mm
LENGTH L153 mm
M3 thread repair tap – STI tap for V-Coil M3x0.5 inserts
Tool dimension table and technical data
| V-COIL M3 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M3 × 0.5 |
| Tolerance class | 4H |
| Tap diameter B | 3.6 mm |
| Overall length L1 | 53 mm |
| Flute length L2 | 13 mm |
| Shank diameter D2 | 4 mm |
| Square drive a | 3.15 mm |
| Pre-drilled hole | Ø3.1 mm |
The V-Coil M3 thread repair tap cuts an STI (Screw Thread Insert) thread for a Helicoil-type insert in a damaged or worn hole. The tool restores a load-bearing seat without increasing the screw size, so once the insert is installed, the hole accepts a standard M3 screw again. The 4 mm shank with a 3.15 mm square drive fits standard hand tap wrenches.
Repairing a stripped M3 thread in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in steel, stainless steel, cast iron, and aluminum, as well as magnesium and plastics. M3 threads strip most frequently in soft metals, while in steel the insert increases the fatigue life of the joint. The repair is suitable for electronic assemblies, RC models, and precision instruments, among other applications where this thread predominates. Predrill the hole with a drill bit Ø3.1 mm for the STI tap. Drill at the upper tolerance limit and tap with coolant to obtain a clean thread profile.
The dimensions of the cut STI thread are specified by DIN 8140-2. The M3 thread repair tap has an overall length L1 of 53 mm and a flute length L2 of 13 mm, and is compatible with V-Coil inserts in lengths from 1.5xD–3xD. A correctly installed insert restores a thread with a load capacity comparable to or greater than the original.
M3 thread repair step by step
From drilling to the nominal thread
Installing an insert is faster and less expensive than replacing the entire assembly, such as an RC model control board.
Thread repair M3 with a wire insert
1Drilling
Hole: Ø3.1 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M3 × 0.5
In a blind hole, remove the broken-off tang before installing the screw
Helicoil M3 tap (STI) – why it is larger than a standard tap
Compensating for the wire thickness of the thread insert
The STI tool differs from a standard M3 tap only in profile size — the 60° angle and 0.5 mm pitch remain metric. The insert wire occupies space on both sides of the profile, so the diameter is D STI = 3 + 1.3 × 0.5 = 3.65 mm; hence the nonstandard 3.6 mm cutting section, which neither an M4 nor an M5 tap can provide. Tolerance class 4H (equivalent to inch class 3B) is also used for screw-locking inserts, while the finished thread after insert installation is class 6H.
Tap compatibility with the V-Coil insert
What must match before starting the repair
✓Matching size: V-Coil M3 insert with a 0.5 mm pitch.
✓Matching hole: prepare a Ø3.1 mm diameter before tapping.
✓Matching version: available M3 insert lengths: 1.5xD–3xD.
▲Required inspection: depth and wall thickness of the component being repaired.
This is not a standard M3 tap
The tool prepares an oversized mounting thread for a V-Coil insert. Do not use it to cut a standard M3 thread without an insert, and do not substitute a standard tap for it when installing an insert.
Frequently asked questions
For the STI tap, use a drill bit Ø3.1 mm, rather than 2.5 mm as for a standard M3 thread. Drill at the upper tolerance limit so the insert fits without binding. Chamfer the hole entrance at 90–120°.
No, the STI thread has a nonstandard diameter 3.65 mm, which neither M4 nor M5 can reproduce. An incorrect thread profile prevents the insert from locking properly in its seat. The cutting diameter of this tool is B = 3.6 mm.
The 4H designation indicates a close STI thread fit class, equivalent to inch class 3B used in aerospace and screw-locking inserts. After the insert is installed, the working thread achieves class 6H.
Tighten with a torque screwdriver to approximately 0.6–1.0 Nm for M3, and approximately 0.3–0.6 Nm for M2.5. A thread restored with an insert is harder than one cut in aluminum because the wire has a minimum tensile strength of 1400 MPa. This allows it to withstand more assembly and disassembly cycles.
Product accessories
Thread repair insert M3x0.5 2xD V-Coil
Reference: 0000010653 In stock > 10 items
€0.34
€0.42 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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