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Description
FINISHED THREADM8 × 1
TOLERANCE4H
PRE-DRILLED HOLEØ8.3 mm
LENGTH L180 mm
M8x1 thread repair tap – STI tap for V-Coil M8x1 inserts
Tool dimension table and technical data
| V-COIL M8x1 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M8 × 1 |
| Tolerance class | 4H |
| Tap diameter B | 9.3 mm |
| Overall length L1 | 80 mm |
| Flute length L2 | 24 mm |
| Shank diameter D2 | 10 mm |
| Square drive a | 8 mm |
| Pre-drilled hole | Ø8.3 mm |
The V-Coil M8x1 thread repair tap cuts an STI (Screw Thread Insert) thread for a Helicoil-type insert with a 60° profile. The tool restores a load-bearing seat in the stripped hole without increasing the size of the bolt itself. Once the insert is installed, the hole again accepts a standard M8x1 bolt without modification. The 10 mm shank with a 8 mm square drive fits standard hand tap wrenches and holders.
Repairing stripped M8x1 threads in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in steel, stainless steel, cast iron, and aluminum, covering common engineering materials. Threads strip most frequently in soft metals, while in steel the insert improves the fatigue life of the joint. Repair applications include, for example, brake and clutch line banjo bolts on motorcycle master cylinders. The hole for the STI tap measures Ø8.3 mm. Drill at the upper tolerance limit and tap with coolant so the wire seats evenly.
The cut STI thread has dimensions conforming to DIN 8140-2, so the M8x1 thread repair tap prepares a seat for any insert complying with this standard — lengths of 1.5xD, 2xD, and 2.5xD are available in the store. The tool measures 80 mm (L1) with a flute length of 24 mm (L2), and the repaired thread carries loads comparable to or greater than the original.
Repairing an M8x1 thread step by step
From drilling to the nominal thread
Repairing with an insert is faster and less expensive than replacing the entire pump body, for example a caliper with a banjo port.
Thread repair M8x1 with a wire insert
1Drilling
Hole: Ø8.3 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M8 × 1
In a blind hole, remove the broken-off tang before installing the screw
M8x1 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 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 = 8 + 1.3 × P = 8 + 1.3 × 1 = 9.3 mm. Therefore, the tool's cutting diameter B is 9.3 mm — a nonstandard value that neither an M9 nor an M10 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 M8x1 insert with a 1 mm pitch.
✓Matching hole: prepare a Ø8.3 mm diameter before tapping.
✓Matching version: available M8x1 insert lengths: 1.5xD, 2xD, 2.5xD.
▲Required inspection: depth and wall thickness of the component being repaired.
This is not a substitute for an M8x1 tap
The tool cuts only an oversized thread for an insert. A standard M8x1 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 STI insert, drill out the hole to Ø8.3 mm, rather than 7 mm as for a standard M8x1 thread. Keep to the upper diameter tolerance limit. Chamfer the entrance at 90–120° to help the tap enter.
No — the STI thread has a nonstandard diameter of 9.3 mm that neither a standard M9 nor an M10 tap can reproduce. The cutting diameter of this tool is B = 9.3 mm. An incorrect profile will prevent the insert from locking properly in place.
Yes — the inner edge of the wire restores the nominal M8 × 1 thread. The minor diameter after installation is approximately 6.92 mm, in accordance with ISO 724. You can install a standard bolt without any modifications.
Yes, but the insert only restores the mechanical M8 × 1 thread in the hole. Banjo connections and bleeder screws are sealed by the seating surface or washer, rather than the thread itself. After repair, check the condition of the seating surface and use new washers.
Product accessories
Thread repair insert M8x1 2.5xD V-Coil
Reference: 0000006044 In stock > 10 items
€0.53
€0.65 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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