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Description
FINISHED THREADM20 × 2.5
TOLERANCE4H
PRE-DRILLED HOLEØ20.5 mm
LENGTH L1113 mm
M20 thread repair tap – STI tap for V-Coil M20x2.5 inserts
Tool dimension table and technical data
| V-COIL M20 THREAD REPAIR TAP | |
|---|---|
| Thread to be repaired | M20 × 2.5 |
| Tolerance class | 4H |
| Tap diameter B | 22.6 mm |
| Overall length L1 | 113 mm |
| Flute length L2 | 33 mm |
| Shank diameter D2 | 16 mm |
| Square drive a | 12.5 mm |
| Pre-drilled hole | Ø20.5 mm |
The V-Coil M20 thread repair tap cuts an STI (Screw Thread Insert) thread for a Helicoil-type insert in a damaged hole. The tool restores a load-bearing threaded hole without increasing the screw size. Once the insert is installed, the hole again accepts a standard screw M20 × 2.5. The 16 mm shank with a 12.5 mm square drive fits typical hand tap wrenches.
Repairing a stripped M20 thread in steel, stainless steel, cast iron, and aluminum
Materials, tips, and limitations
The tool works in steel, stainless steel, cast iron, and aluminum. Threads strip most often in soft metals, while in steel the insert improves the fatigue life of the joint. The M20 size is used, for example, in large machine structures and housings, where the material surrounding the threaded hole determines the load capacity of property class 8.8 bolts. The pilot hole is made with a drill bit Ø20.5 mm for the STI tap. Drill at the upper tolerance limit and tap with coolant to obtain a clean, repeatable profile.
The cut STI thread has dimensions conforming to DIN 8140-2, so the M20 thread repair tap prepares a hole for any insert conforming to this standard — lengths of 2xD are available in the store. The tool measures 113 mm (L1) with a flute length of 33 mm (L2), and the repaired thread carries loads comparable to or greater than those of the original.
M20 thread repair step by step
From drilling to the nominal thread
Repairing with an insert costs a fraction of reconditioning the entire housing and involves a few simple steps.
Thread repair M20 with a wire insert
1Drilling
Hole: Ø20.5 mm
2Chamfering the hole entrance
Angle: 90–120°
3STI tapping
With coolant, 4H
4Insert installation
Tang: break off
✓Nominal thread
Screw: M20 × 2.5
In a blind hole, remove the broken-off tang before installing the screw
Helicoil M20 tap (STI) – why it is larger than a standard tap
Compensating for the wire thickness of the thread insert
The STI tool differs from a standard M20 tap only in profile size — the 60° angle and 2.5 mm pitch remain metric. The insert wire occupies space on both sides of the profile, so the diameter is D STI = 20 + 1.3 × 2.5 = 23.25 mm; hence the nonstandard 22.6 mm cutting section, which neither an M22 nor an M24 tap can provide. Tolerance class 4H (equivalent to inch class 3B) is also used for screw-locking inserts, while the finished thread after insert installation is class 6H.
Tap compatibility with the V-Coil insert
What must match before starting the repair
✓Matching size: V-Coil M20 insert with a 2.5 mm pitch.
✓Matching hole: prepare a Ø20.5 mm diameter before tapping.
✓Matching version: available M20 insert lengths: 2xD.
▲Required inspection: depth and wall thickness of the component being repaired.
This is not a substitute for an M20 tap
The tool cuts only an oversized thread for an insert. A standard M20 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 tap, use a drill bit Ø20.5 mm, rather than the 17.5 mm required for a standard M20 thread. Drill the hole at the upper tolerance limit so the insert seats without binding. Chamfering the hole entrance at 90–120° is recommended.
No, the STI thread has a nonstandard diameter 23.25 mm, which neither M22 nor M24 can reproduce. An incorrect profile prevents the insert from locking properly in the hole. The cutting diameter of this tool is B = 22.6 mm.
The designation 4H indicates a close-fit STI thread tolerance class, corresponding to inch thread class 3B used in aerospace and with screw-locking inserts. After the insert is installed, the finished thread meets class 6H, compatible with standard M20 screws.
Yes. The free-running version is secured with threadlocker or a self-locking nut. For severe vibration, screw-locking inserts are available in accordance with DIN 8140 form B, with a polygonal turn that locks the screw.
Product accessories
Drill 20.5 Cobalt NWKc HSSE DIN 345
Reference: 0000008560 In stock < 10 items
€35.53
€43.70 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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