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Description
FINISHED THREADM10 × 1.25
TOLERANCE4H
PRE-DRILLED HOLEØ10.3 mm
LENGTH L185 mm
M10x1.25 thread repair tap – STI tap for V-Coil M10x1.25 inserts
Tool dimension table and technical data
| V-COIL M10x1.25 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M10 × 1.25 |
| Tolerance class | 4H |
| Tap diameter B | 11.6 mm |
| Overall length L1 | 85 mm |
| Flute length L2 | 25 mm |
| Shank diameter D2 | 8 mm |
| Square drive a | 6.3 mm |
| Pre-drilled hole | Ø10.3 mm |
The V-Coil M10x1.25 thread repair tap cuts an STI (Screw Thread Insert) thread for a Helicoil-type insert. The tool restores a load-bearing threaded hole without increasing the screw size, and once the insert is installed, the hole accepts a standard M10x1.25 screw. The 60° profile corresponds to a metric thread. The 8 mm square shank with a 6.3 mm square drive fits typical hand tap wrenches.
Repairing stripped M10x1.25 threads in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in steel, stainless steel, cast iron, and aluminum. Threads strip most often in soft metals, so the insert provides the greatest benefit in aluminum, while in steel it improves the fatigue life of the joint. The M10x1.25 size is found, for example, in engine bolts and accessory mountings, where maintaining the tightening torque matters. The hole diameter for the STI tap is Ø10.3 mm; drill at the upper tolerance limit and tap with coolant.
The dimensions of the cut STI thread are specified by DIN 8140-2. The M10x1.25 thread repair tap has an overall length L1 of 85 mm and a flute length L2 of 25 mm, and is compatible with V-Coil inserts in lengths of 2xD and 3xD. A correctly installed insert restores a thread with a load capacity comparable to or greater than the original.
Repairing an M10x1.25 thread step by step
From drilling to the nominal thread
Repairing with an insert is faster and less expensive than replacing the entire component, and for engine bolts it preserves the original size and tightening torque.
Thread repair M10x1.25 with a wire insert
1Drilling
Hole: Ø10.3 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M10 × 1.25
In a blind hole, remove the broken-off tang before installing the screw
M10x1.25 Helicoil tap (STI) – why it is larger than a standard tap
Compensating for the wire thickness of the thread insert
The STI thread retains the pitch P = 1.25 mm and the 60° thread angle of the ISO metric thread, but its diameter is intentionally enlarged. The increase compensates for the insert wire thickness on both sides of the profile, according to the following relationship: D STI = 10 + 1.3 × P = 10 + 1.3 × 1.25 = 11.62 mm. Therefore, the tool's cutting diameter B is 11.6 mm — a nonstandard value that neither an M11 nor an M12 tap can provide. The 4H tolerance corresponds to inch thread class 3B and is also suitable for screw-locking inserts; once the insert is installed, the finished thread achieves the standard 6H class.
Tap compatibility with the V-Coil insert
What must match before starting the repair
✓Matching size: V-Coil M10x1.25 insert with a 1.25 mm pitch.
✓Matching hole: prepare a Ø10.3 mm diameter before tapping.
✓Matching version: available M10x1.25 insert lengths: 2xD, 3xD.
▲Required inspection: depth and wall thickness of the component being repaired.
This is not a substitute for an M10x1.25 tap
The tool cuts only an oversized thread for an insert. A standard M10x1.25 bolt will not engage in a hole tapped this way without an insert, and a standard tap will not prepare the hole for an insert.
Frequently asked questions
For the insert, use a drill bit Ø10.3 mm, because the STI thread has a larger diameter than a standard M10x1.25 thread, for which 8.8 mm is sufficient. Drill at the upper tolerance limit and chamfer the hole entrance at 90–120°. This facilitates tap entry and insert installation.
The STI tap cuts a larger profile — the major diameter is approximately 11.62 mm instead of 10 mm, an increase of twice the 0.81 mm wire thickness. The 1.25 mm pitch and 60° angle remain the same as on a standard tap. Thanks to DIN 8140, inserts from Helicoil, V-Coil, Recoil, and BaerCoil are interchangeable.
Yes. The inner edge of the wire recreates the nominal M10 × 1.25 thread, so a standard screw can be installed without any modifications. The minor diameter after installation is approximately 8.65 mm, in accordance with ISO 724.
Yes. Threaded holes that are frequently disassembled, such as those for spark plugs and fittings, are a typical application for inserts. The hard stainless steel wire with an Rm of at least 1400 MPa withstands repeated assembly without thread wear and reduces galvanic corrosion in the aluminum cylinder head.
Product accessories
Thread repair insert M10x1.25 3xD V-Coil
Reference: 0000006050 In stock > 10 items
€0.71
€0.87 brutto
Thread repair insert M10x1.25 2xD V-Coil
Reference: 0000007947 In stock > 10 items
€0.47
€0.58 brutto
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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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