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Description
THREAD BEING REPAIREDM8x1.25
THREAD FOR INSERT9.6 mm
INSERT HEIGHT12.0 mm
NUMBER OF REPAIRS15
M8 thread repair kit – 1.5xD helicoil-type inserts
Kit with drill bit, STI tap, installation tool and 15 inserts
| KIT DATA | |
|---|---|
| Thread to be repaired | M8x1.25 |
| Inserts included | 15 pcs |
| Insert length | 1.5xD = 12.0 mm |
| Drill bit | Ø8.3 mm |
| Tap | STI M8x1.25 HSS-G |
| Insert material | stainless steel |
| Manufacturer | Varel |
| Product code | 010619 |
The M8 thread repair kit restores a load-bearing threaded hole M8x1.25 in an engine, gearbox or machine housing without drilling for a larger bolt size. The kit includes a drill bit, STI tap, installation tool, punch and 15 stainless steel 1.5xD inserts.
Contents of the M8 thread repair kit
Four tools and a set of inserts in a case
Ø8.3 mm drill bit
HSS, DIN 338 – 1 pcs
M8 STI tap
HSS-G – 1 pcs
M8x1.25 inserts
1.5xD, stainless steel – 15 pcs
Installation tool
tool steel – 1 pcs
Punch
breaks off the tang – 1 pcs
The tools in the case can handle many repairs — only the inserts are consumed. Once they run out, only M8x1.25 1.5xD thread inserts need to be purchased.
Technical data for the STI tap and 1.5xD insert
Dimensions of both kit components
| STI M8x1.25 TAP | |
|---|---|
| Thread to be repaired | M8x1.25 |
| Thread pitch P | 1.25 mm |
| Thread diameter B | 9.6 mm |
| Overall length L1 | 80 mm |
| Flute length | 24 mm |
| Square drive | 8.0 mm |
| Material | HSS-G (ground thread) |
| Tap drill hole | Ø8.3 mm |
| Hole type | through and blind |
| M8x1.25 1.5xD INSERT | |
|---|---|
| Restored thread | M8x1.25 |
| Thread pitch P | 1.25 mm |
| Height after installation | 12.0 mm (1.5xD) |
| Thread count | approximately 7.4 |
| Free-state outside diameter | 9.85–10.35 mm |
| Material | stainless steel |
| Installation version | with tang |
| Recommended drill bit | Ø8.3 mm |
| Thread direction | right-handed |
Twelve millimeters of insert length and 7.4 threads transfer the M8 bolt load deep into the material. This length suits steel, stainless steel, cast iron and aluminum, while the stainless steel coil separates the steel bolt from the aluminum housing, reducing galvanic corrosion and thread galling.
How the M8x1.25 thread insert works
Comparison of a directly tapped thread and a thread with an insert
| What changes in the threaded hole | Standard M8 thread | Thread for insert |
|---|---|---|
| Tap drill | 6.8 mm | 8.3 mm |
| Thread cut in the parent material | 8.0 mm | 9.63 mm |
| Tap | M8 | M8 STI |
| Bolt after repair | M8 | M8 |
The insert is a resilient coil wound from wire with a diamond-shaped cross section. The outer point of the diamond engages the enlarged thread in the hole, while the inner point restores the standard thread M8x1.25. The repair therefore does not change the bolt or the tightening torque specified in the machine documentation.
A pitch of 1.25 mm means a wire thickness of 0.65 × 1.25 = 0.81 mm. The wire sits on both sides of the profile, so the thread in the parent material increases to 8 + 1.3 × 1.25 = 9.63 mm. It is cut by the tap M8 STI with a 9.6 mm thread, working in a hole 8.3 mm instead of 6.8 mm.
The joint requires no adhesive. In its free state, the insert measures 9.85–10.35 mm, so once the tool is released it expands against the thread in the parent material and stays in place even when the bolt is unscrewed.
Installing an insert in an M8 hole – sequence of operations
Four steps from drilling to a finished threaded hole
M8 thread repair step by step
1Drilling
Diameter: Ø8.3 mm
2Tapping
Tap: M8 STI
3Screwing in the insert
With the installation tool, a quarter turn below the surface
✓Breaking off the tang
Finished thread: M8x1.25
Tap with oil, reversing the tool after each full turn
▲
Aluminum requires controlled tightening torque
The insert reinforces the thread, but the load capacity of the joint is still limited by the parent material. In an aluminum housing, tighten the M8 bolt with a torque wrench according to the machine documentation — higher torque will pull out the insert together with the thread in the parent material.
The M8 STI tap has an overall length of 80 mm and a flute length of 24 mm. The 8.0 mm square drive fits a standard tap wrench, and tapping oil significantly reduces resistance at this diameter.
Assessing the condition of the hole takes a moment but determines the outcome. If cracks or material deformed by a pulled-out bolt are visible around the hole, the insert will not restore load capacity — it relies on a thread cut in that same material. A sound wall around the hole is essential for the repair.
M8 thread repair – customer questions
Selecting tools, drill bit and insert length
Frequently asked questions
No. The hole for the insert must have a 9.63 mm thread, which is 1.63 mm larger in diameter than a standard M8 thread. Only the STI tap in the kit, marked 9.6 mm, cuts this oversize thread.
Ø8.3 mm — the drill bit is included. A standard M8 thread requires a 6.8 mm drilled hole, so the hole increases by 1.5 mm and usually removes the entire damaged thread.
Yes. The stainless steel wire is harder than aluminum, so the thread stops wearing out during repeated disassembly, and the steel bolt does not contact the aluminum directly, reducing galvanic corrosion.
Yes, provided the insert is installed to its full depth and the material around the hole is sound. The joint usually withstands more than the original thread because the load is distributed more evenly over 7.4 threads.
Fifteen — that is how many inserts the kit contains. For repeated repairs, it is worth keeping a spare STI tap, as it is the most heavily loaded tool in the kit.
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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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