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Description
THREAD BEING REPAIREDM3x0.5
THREAD FOR INSERT3.6 mm
INSERT HEIGHT4.5 mm
NUMBER OF REPAIRS15
M3 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 | M3x0.5 |
| Inserts included | 15 pcs |
| Insert length | 1.5xD = 4.5 mm |
| Drill bit | Ø3.1 mm |
| Tap | STI M3x0.5 HSS-G |
| Insert material | stainless steel |
| Manufacturer | Varel |
| Product code | 13961 |
The M3 thread repair kit restores a stripped or worn thread M3x0.5 without increasing the bolt size — after repair, the same M3 bolt is used in the hole. The kit contains all the tools needed for the repair and 15 stainless steel inserts, enough for fifteen holes.
Contents of the M3 thread repair kit
Four tools and a set of inserts in a case
Ø3.1 mm drill bit
HSS, DIN 338 – 1 pcs
M3 STI tap
HSS-G, – 1 pcs
M3x0.5 inserts
1.5xD, stainless steel – 15 pcs
Installation tool
tool steel – 1 pcs
Punch
breaks off the tang – 1 pcs
The tools in the kit are reusable; only the inserts are consumed. Once they run out, only M3x0.5 1.5xD thread inserts need to be purchased, without buying the complete kit again.
Technical data for the STI tap and 1.5xD insert
Dimensions of both kit components
| STI M3x0.5 TAP | |
|---|---|
| Thread to be repaired | M3x0.5 |
| Thread pitch P | 0.5 mm |
| Thread diameter B | 3.6 mm |
| Overall length L1 | 53 mm |
| Flute length | 13 mm |
| Square drive | 2.8 mm |
| Material | HSS-G (ground thread) |
| Tap drill hole | Ø3.1 mm |
| Hole type | through and blind |
| M3x0.5 1.5xD INSERT | |
|---|---|
| Restored thread | M3x0.5 |
| Thread pitch P | 0.5 mm |
| Height after installation | 4.5 mm (1.5xD) |
| Thread count | approximately 6.3 |
| Free-state outside diameter | 3.8–4.35 mm |
| Material | stainless steel |
| Installation version | with tang |
| Recommended drill bit | Ø3.1 mm |
| Thread direction | right-handed |
The 1.5xD inserts in the kit have a general-purpose length — they work in steel, stainless steel, cast iron and aluminum, the materials used for most threaded holes being repaired. Approximately 6.3 threads distribute the bolt load over the full thread depth. The stainless steel wire also separates the steel bolt from the aluminum, reducing galvanic corrosion and thread galling.
How the M3x0.5 thread insert works
Comparison of a directly tapped thread and a thread with an insert
| What changes in the threaded hole | Standard M3 thread | Thread for insert |
|---|---|---|
| Tap drill | 2.5 mm | 3.1 mm |
| Thread cut in the parent material | 3.0 mm | 3.65 mm |
| Tap | M3 | M3 STI |
| Bolt after repair | M3 | M3 |
The insert is a resilient coil wound from wire with a diamond-shaped cross section — also called a thread repair bushing or spring in the workshop. The outer edge of the diamond anchors in the oversize thread cut in the parent material, while the inner edge provides the bolt with a standard thread M3x0.5. The last row of the table is the most important: after repair, the same bolt, the same wrench and the same tightening torque are used.
The oversize dimensions in the first two rows come directly from the wire thickness. The wire is approximately 0.65 times the pitch, or 0.65 × 0.5 = 0.33 mm. The thread in the parent material must accommodate it on both sides of the profile, so its diameter increases to 3 + 1.3 × 0.5 = 3.65 mm. Hence the tap M3 STI with a 3.6 mm thread and the drill bit 3.1 mm instead of 2.5 mm. A standard M3 tap cannot replace the STI tap — the insert would have no thread to lock into.
The insert holds without adhesive. In its free state, its outside diameter is 3.8–4.35 mm, larger than the thread in the parent material. The installation tool compresses the coils as the insert is screwed in; once the torque is released, the coils expand and lock into the hole.
Installing an insert in an M3 hole – sequence of operations
Four steps from drilling to a finished threaded hole
M3 thread repair step by step
1Drilling
Diameter: Ø3.1 mm
2Tapping
Tap: M3 STI
3Screwing in the insert
With the installation tool, a quarter turn below the surface
✓Breaking off the tang
Finished thread: M3x0.5
Tap with oil, reversing the tool after each full turn
▲
Blind hole – remove the broken-off tang
The tang broken off with the punch remains at the bottom of the hole. Remove it with a magnet or tweezers — if left in place, it blocks the bolt and prevents full tightening. In a blind hole, also tap deeper than the height of the insert.
A tap with a diameter of 3.6 mm is easy to break. Guide it perpendicular to the surface using a tap wrench fitted to the 2.8 mm square drive, and check alignment from two sides during the first few threads.
M3 thread repair – customer questions
Selecting tools, drill bit and insert length
Frequently asked questions
No. The insert requires a thread enlarged by twice the wire thickness, or approximately 0.65 mm in diameter. This is why the tap in the kit measures 3.6 mm rather than 3 mm. In a thread cut with a standard M3 tap, the insert has no thread to lock into.
Ø3.1 mm — this drill bit is included in the kit. A standard M3 thread requires a 2.5 mm drilled hole, so the hole for the insert is 0.6 mm larger. The stripped M3 thread usually falls within this allowance, so the repair does not require prior enlargement of the hole.
No, the standard M3 bolt is retained. The inner surface of the insert restores the nominal M3x0.5 thread, so the same bolt used before the hole was damaged still fits. Neither the wrench size nor the tightening torque changes.
Fifteen — that is how many inserts the kit contains. The drill bit, tap, installation tool and punch are reusable, so once the inserts are used up, only M3x0.5 inserts need to be purchased. For repeated repairs, it is worth keeping a spare tap, as at a diameter of 3.6 mm it is the tool most susceptible to damage.
In steel, stainless steel, cast iron and aluminum, the standard length of 1.5xD, or 4.5 mm, is fully sufficient. A 2xD or 2.5xD insert is used in heavily loaded joints and in materials with low shear strength, such as magnesium or plastics — the longer insert distributes the load over more threads in the hole.
Product accessories
Thread repair insert M3x0.5 2xD V-Coil
Reference: 0000010653 In stock > 10 items
€0.34
€0.42 brutto
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Shipping
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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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