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Description
THREAD BEING REPAIREDM12x1.75
THREAD FOR INSERT14.2 mm
INSERT HEIGHT18.0 mm
NUMBER OF REPAIRS10
M12 thread repair kit – 1.5xD helicoil-type inserts
Kit with drill bit, STI tap, installation tool and 10 inserts
| KIT DATA | |
|---|---|
| Thread to be repaired | M12x1.75 |
| Inserts included | 10 pcs |
| Insert length | 1.5xD = 18.0 mm |
| Drill bit | Ø12.4 mm |
| Tap | STI M12x1.75 HSS-G |
| Insert material | stainless steel |
| Manufacturer | Varel |
| Product code | 13964 |
The M12 thread repair kit covers the largest size in this range — tapped holes M12x1.75 in frames, flanges, and machine bases. The same M12 screw is reused after repair, and the kit includes 10 stainless steel 1.5xD inserts and all the tools required for the job.
Contents of the M12 thread repair kit
Four tools and a set of inserts in a case
Ø12.4 mm drill bit
HSS, DIN 338 – 1 pcs
M12 STI tap
HSS-G – 1 pcs
M12x1.75 inserts
1.5xD, stainless steel – 10 pcs
Installation tool
tool steel – 1 pcs
Punch
breaks off the tang – 1 pcs
The M12 kit contains ten inserts rather than fifteen as in the smaller sizes — each insert uses more material. The tools remain reusable; only M12x1.75 inserts need to be purchased.
Technical data for the STI tap and 1.5xD insert
Dimensions of both kit components
| STI M12x1.75 TAP | |
|---|---|
| Thread to be repaired | M12x1.75 |
| Thread pitch P | 1.75 mm |
| Thread diameter B | 14.2 mm |
| Overall length L1 | 95 mm |
| Flute length | 30 mm |
| Square drive | 9.0 mm |
| Material | HSS-G (ground thread) |
| Tap drill hole | Ø12.4 mm |
| Hole type | through and blind |
| M12x1.75 1.5xD INSERT | |
|---|---|
| Restored thread | M12x1.75 |
| Thread pitch P | 1.75 mm |
| Height after installation | 18.0 mm (1.5xD) |
| Thread count | approximately 8.4 |
| Free-state outside diameter | 14.4–15.0 mm |
| Material | stainless steel |
| Installation version | with tang |
| Recommended drill bit | Ø12.4 mm |
| Thread direction | right-handed |
Eighteen millimeters in height and 8.4 coils provide the largest load-bearing area in this range of kits. The 1.5xD length is suitable for steel, stainless steel, cast iron, and aluminum, while the stainless steel wire protects the joint against thread seizure.
How the M12x1.75 thread insert works
Comparison of a directly tapped thread and a thread with an insert
| What changes in the threaded hole | Standard M12 thread | Thread for insert |
|---|---|---|
| Tap drill | 10.2 mm | 12.4 mm |
| Thread cut in the parent material | 12.0 mm | 14.28 mm |
| Tap | M12 | M12 STI |
| Bolt after repair | M12 | M12 |
The insert is a coil wound from diamond-section wire. The outer edge anchors in the oversized thread in the material, while the inner edge restores the standard thread M12x1.75 — the last row of the table shows that the screw side remains unchanged.
A pitch of 1.75 mm gives a wire thickness of 0.65 × 1.75 = 1.14 mm. On both sides of the profile, this increases the thread in the material to 12 + 1.3 × 1.75 = 14.28 mm, which is the tap diameter M12 STI. The hole for it measures 12.4 mm instead of 10.2 mm for a standard M12 thread.
Retention relies on the resilience of the coil. The free insert measures 14.4–15.0 mm, so once the tool is released, it expands against the thread in the hole with enough force to withstand repeated screw removal.
Installing an insert in an M12 hole – sequence of operations
Four steps from drilling to a finished threaded hole
M12 thread repair step by step
1Drilling
Diameter: Ø12.4 mm
2Tapping
Tap: M12 STI
3Screwing in the insert
With the installation tool, a quarter turn below the surface
✓Breaking off the tang
Finished thread: M12x1.75
Tap with oil, reversing the tool after each full turn
▲
Tapping 14.28 mm requires force and cooling
At this diameter, the tap removes a large amount of material, and the cutting edge temperature rises quickly. Use tapping oil, reverse the tool after each full turn, and do not apply axial pressure — the tap feeds itself into the material. In cast iron, use compressed air instead of oil.
The M12 STI tap has an overall length of 95 mm, a flute length of 30 mm, and a 9.0 mm square. A tap wrench with a longer handle is required — the tapping torque is considerably higher here than for M8.
At this diameter, it is advisable to work in two passes: first drill a pilot hole at half the diameter, then enlarge it to 12.4 mm. The smaller drill bit is easier to guide, and the resulting hole is free of taper, ensuring even coil contact with a 18 mm insert.
M12 thread repair – customer questions
Selecting tools, drill bit and insert length
Frequently asked questions
This is what the manufacturer's catalog specifies for sizes M12 and larger. A single M12x1.75 insert uses more wire than three M4 inserts, so the kit contains fewer inserts at a similar total weight.
Ø12.4 mm — the drill bit is included in the kit. A standard M12x1.75 thread requires a 10.2 mm hole, so the hole diameter increases by 2.2 mm and removes even a severely stripped thread.
No. The insert requires a 14.28 mm thread, 2.28 mm larger in diameter than a standard M12 thread. Only the STI tap supplied in the kit cuts this profile.
Yes, the STI tap works in both through holes and blind holes. In a through hole, after breaking off the tang, simply check that the insert has not moved past the bottom edge of the material.
For heavily loaded joints and in materials with low shear strength, such as magnesium or plastics. The 2xD and 2.5xD versions distribute pressure over more threads in the hole.
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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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