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Description
FINISHED THREADM9 × 1.25
TOLERANCE4H
PRE-DRILLED HOLEØ9.3 mm
LENGTH L185 mm
M9x1.25 thread repair tap – STI tap for V-Coil M9x1.25 inserts
Tool dimension table and technical data
| V-COIL M9x1.25 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M9 × 1.25 |
| Tolerance class | 4H |
| Tap diameter B | 10.6 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 | Ø9.3 mm |
The V-Coil M9x1.25 thread repair tap cuts an STI (Screw Thread Insert) thread for a Helicoil-type insert. The tool restores a load-bearing seat without increasing the bolt size. Once the insert is installed, the hole again accepts a standard M9x1.25 bolt, so there is no need to switch to a larger size. The 8 mm shank with a 6.3 mm square drive fits standard hand tap wrenches and allows the tap to be guided in line with the hole axis.
Repairing stripped M9x1.25 threads in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in steel, stainless steel, cast iron, and aluminum, so a single tap handles different materials. Threads strip most frequently in soft metals, while in steel the insert improves the fatigue life of the joint. M9x1.25 is a special size found, for example, in repairs to nonstandard structures and older equipment. Make the pilot hole with a drill bit Ø9.3 mm for the STI tap, drill at the upper tolerance limit, and tap with coolant.
The M9x1.25 thread repair tap cuts an STI thread with dimensions conforming to DIN 8140-2. The tool's overall length L1 is 85 mm, and its flute length L2 is 25 mm. The tool is compatible with V-Coil inserts in lengths of 2xD, and a properly repaired thread carries loads comparable to or greater than the original thread.
Repairing an M9x1.25 thread step by step
From drilling to the nominal thread
Repairing with an insert is faster and less expensive than replacing the entire part, which is particularly important with the uncommon M9x1.25 size.
Thread repair M9x1.25 with a wire insert
1Drilling
Hole: Ø9.3 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M9 × 1.25
In a blind hole, remove the broken-off tang before installing the screw
M9x1.25 Helicoil 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 1.25 mm pitch — only the size changes. The diameter increases by twice the insert wire thickness: D STI = 9 + 1.3 × 1.25 = 10.62 mm. This is why the tool's cutting section measures 10.6 mm, and neither an M10 nor an M11 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 M9x1.25 insert with a 1.25 mm pitch.
✓Matching hole: prepare a Ø9.3 mm diameter before tapping.
✓Matching version: available M9x1.25 insert lengths: 2xD.
▲Required inspection: depth and wall thickness of the component being repaired.
This is not a standard M9x1.25 tap
The tool prepares an oversized mounting thread for a V-Coil insert. Do not use it to cut a standard M9x1.25 thread without an insert, and do not substitute a standard tap for it when installing an insert.
Frequently asked questions
For the STI thread, use a drill bit Ø9.3 mm, which is larger than the 7.8 mm required for a standard M9x1.25 thread. Drill at the upper tolerance limit so the insert can enter freely. Chamfer the entrance at 90–120°.
The STI tap cuts a larger thread with a major diameter of approximately 10.62 mm instead of 9 mm, because twice the 0.81 mm wire thickness is added. The 1.25 mm pitch and 60° angle remain the same as on a standard tap. The resulting seat accepts interchangeable Helicoil, V-Coil, Recoil, and BaerCoil inserts in accordance with DIN 8140.
The designation 4H indicates a close-fit class for STI threads, equivalent to inch class 3B used in aerospace applications and with screw-locking inserts. Once the insert is installed, the finished thread meets class 6H, the standard for typical bolts.
After the insert is installed, the thread returns to its nominal size M9x1.25, so the existing bolt fits. Bolts of this size are available from fastener distributors as a special size.
Product accessories
Thread repair insert M9x1.25 2xD V-Coil
Reference: 0000007492 In stock > 10 items
€0.53
€0.65 brutto
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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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