Helicoil Tap Drill Chart: Metric STI Drill Sizes for Wire Inserts
A helicoil tap drill chart helps buyers choose the correct drill diameter before using an STI tap for wire thread insert installation. STI tap drill sizes are different from standard tap drill sizes because a wire insert repair requires an oversized installation thread.
The main quick-reference table gives common metric STI drill references for M3, M4, M5, M6, M8, M10, and M12. This page also covers selected smaller and larger metric coarse sizes. For these sizes, confirm drill values against the selected insert and STI tap system.
For common metric wire thread insert repairs, typical STI drill references include M6 × 1.0 at 6.3 mm and M8 × 1.25 at 8.3 mm. Treat these values as RFQ references and confirm final dimensions with the actual insert system, STI tap data, material, and repair condition.
Use this helicoil tap drill chart to prepare quotations, repair kit labels, and sample kit specifications. Do not use a standard tap drill chart for wire thread insert repair unless the insert supplier confirms it.
Metric Helicoil Tap Drill Chart
The table below lists common metric coarse STI tap drill references for wire thread insert repair and kit preparation. These values are practical quotation references, not universal process approval.
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| Original Thread | Pitch | Common STI Tap Drill Reference | Matching STI Tap | Common Insert Lengths | Typical Use |
|---|---|---|---|---|---|
| M3 | 0.5 mm | 3.1 mm | M3 × 0.5 STI tap | 1D, 1.5D, 2D | Small parts, light repair kits, electronics, compact housings. |
| M4 | 0.7 mm | 4.2 mm | M4 × 0.7 STI tap | 1D, 1.5D, 2D | Small machinery, covers, aluminum housings, maintenance kits. |
| M5 | 0.8 mm | 5.2 mm | M5 × 0.8 STI tap | 1D, 1.5D, 2D | General repair, light equipment, automotive and distributor kits. |
| M6 | 1.0 mm | 6.3 mm | M6 × 1.0 STI tap | 1D, 1.5D, 2D | Common repair kit size for maintenance and industrial repair. |
| M8 | 1.25 mm | 8.3 mm | M8 × 1.25 STI tap | 1D, 1.5D, 2D | Machinery, automotive repair, equipment maintenance, kit programs. |
| M10 | 1.5 mm | 10.4 mm | M10 × 1.5 STI tap | 1D, 1.5D, 2D | Industrial maintenance, stronger repair cases, professional kits. |
| M12 | 1.75 mm | 12.4 mm | M12 × 1.75 STI tap | 1D, 1.5D, 2D | Heavier repair work, machinery parts, industrial repair programs. |
Additional Metric Coarse STI Sizes: M2 to M20
Metric coarse STI tap and insert systems also extend beyond the M3–M12 quick-reference range. For the sizes below, confirm the drill value from the selected insert/STI system before controlled machining or kit labeling.
Why Can Helicoil STI Tap Drill Charts Show Different Values?
Different published technical sources may show slightly different drill references for the same nominal metric thread. That does not automatically mean one chart is wrong. Recommended preparation can depend on the insert system, STI tap geometry, tolerance, material, repair condition and manufacturer-controlled data.
M6 × 1.0 Example
This page uses 6.3 mm as a common M6 × 1.0 repair reference. Other published systems may show a nearby value. For controlled work, follow the actual insert and STI tap specification.
M8 × 1.25 Example
This page uses 8.3 mm as a common M8 × 1.25 repair reference. Do not replace approved system data solely because a generic chart shows another nearby number.
Quick Answers for Common Metric Sizes
These short answers help buyers check common metric repair sizes before sending a quotation request.
M4 Helicoil Drill Size
For M4 × 0.7 wire thread insert repair, 4.2 mm is a common STI drill reference. Confirm the M4 × 0.7 STI tap before ordering.
M5 Helicoil Drill Size
For M5 × 0.8 wire thread insert repair, 5.2 mm is a common STI drill reference. Specify insert length and kit contents in the RFQ.
M6 Helicoil Drill Size
For M6 × 1.0 wire thread insert repair, 6.3 mm is a common STI drill reference. See the dedicated M6 guide.
M8 Helicoil Drill Size
For M8 × 1.25 wire thread insert repair, 8.3 mm is a common STI drill reference. See the dedicated M8 guide.
M10 Helicoil Drill Size
For M10 × 1.5 wire thread insert repair, 10.4 mm is a common STI drill reference. Confirm hole depth and repair load.
M12 Helicoil Drill Size
For M12 × 1.75 wire thread insert repair, 12.4 mm is a common STI drill reference. Confirm tool access before repair.
M16 Helicoil Drill Size
M16 × 2.0 is a common metric coarse insert size. Use the selected M16 STI tap and insert system to confirm the receiving-hole / drill reference before controlled machining.
M20 Helicoil Drill Size
M20 × 2.5 is a common metric coarse insert size. Confirm the drill and STI tapping data from the actual large-size insert system rather than scaling a smaller-size chart.
STI Tap Required
Wire thread inserts require a matching STI tap. A standard metric tap does not create the correct installation thread for the insert.
Kit RFQ Required
For repair kits, specify inserts, drill bit, STI tap, installation tool, tang break tool, case, label, barcode, and refill pack requirement.
Helicoil Tap Drill Chart vs Standard Tap Drill Chart
A common repair failure is using a standard tap drill chart for a wire thread insert repair. The drilled hole and tap process are different because the final internal thread is created by the installed insert, not directly by a standard tap.
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| Item | Standard Tap Drill Chart | STI Tap Drill Chart | Buyer Decision |
|---|---|---|---|
| Purpose | Prepares a hole for a normal internal thread. | Prepares a hole before STI tapping for wire inserts. | Use STI chart for insert repair |
| Tap Type | Uses standard machine taps, hand taps, or forming taps. | Uses STI taps designed for screw thread insert installation. | Do not substitute |
| Final Thread | The tap directly creates the final internal thread. | The STI tap creates the installation thread that holds the insert. | Different process |
| Repair Kit Use | Not enough for wire insert repair kit design. | Required for matching drill, STI tap, insert, and tools. | Use for kit design |
| Common Mistake | Buyer drills the wrong hole size for insert installation. | Buyer still must confirm insert length, type, and tool access. | Confirm before bulk order |
Example: M6 × 1.0
A normal M6 × 1.0 tapped thread and an M6 × 1.0 wire-insert repair are different operations. The wire-insert repair uses the matching STI receiving thread before the insert is installed.
Example: M8 × 1.25
A normal M8 × 1.25 tap drill should not be substituted for the M8 wire-insert STI preparation. Confirm the matching drill, STI tap and insert system together.
Drill Size Is Only the First Step
A correct drill reference does not complete a wire thread insert repair. The receiving thread, inspection and installation stages must also match the selected system.
Drill
Prepare the hole using the approved STI drill / receiving-hole reference.
STI Tap
Create the insert receiving thread with the matching STI tap and process.
Inspect
Check the STI thread using the drawing or insert-system inspection requirement.
Install
Install the correct wire insert with the matched tool and specified depth.
How to Specify Drill, STI Tap and Insert Together
A correct RFQ should not separate drill size, tap type, and insert size. These parts must match as one repair system, especially for distributor repair kits and private-label kit programs.
Confirm Thread
State metric, UNC, UNF, or other thread standard, plus original screw size and pitch.
Select STI Drill
Use the STI tap drill reference for the insert system, not a standard tap drill value.
Match STI Tap
Specify the matching STI tap size, flute style, coating, and target parent material if needed.
Build the Kit
Define inserts, drill bit, STI tap, installation tool, tang break tool, case, label, and refill packs.
Common Tap Drill Selection Mistakes
Tap drill mistakes can cause difficult STI tapping, weak insert retention, poor screw fit, or failed repair. Buyers should confirm the full repair system before comparing kit price.
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| Mistake | Why It Creates Risk | Better Practice |
|---|---|---|
| Using a standard drill chart | The drilled hole may not fit the STI tap system required for wire inserts. | Use the STI tap drill chart for wire thread insert repairs. |
| Only quoting thread diameter | Pitch, insert length, and tool set remain undefined. | Quote thread size, pitch, length, drill, STI tap, and tools together. |
| No material information | Material affects drilling, tapping, chip control, and final retention. | Provide aluminum, steel, stainless steel, cast iron, or other material details. |
| No tool access review | Deep or restricted holes may be difficult to drill, tap, or install. | Confirm hole depth, part geometry, and installation clearance. |
| Wrong repair kit contents | The kit may include inserts but not the correct drill bit or STI tap. | Define every kit component before sample approval. |
What Buyers Should Send Before Quotation
A helicoil tap drill chart helps with early selection, but the supplier still needs complete technical and commercial details before quoting inserts, STI taps, tools, or repair kits.
Thread Details
- Thread standard and original screw size.
- Pitch and tolerance requirement if known.
- Parent material and hole condition.
- Existing insert / branded system reference if replacing a current repair system.
- Repair, reinforcement, or production use.
Insert and Tool Details
- Insert length and insert type.
- STI tap and drill bit requirement.
- Installation tool and tang break tool requirement.
- Extractor or removal tool requirement if needed.
Order Details
- Loose inserts, refill packs, or complete kits.
- Quantity by size.
- Case type, label, manual, barcode, and logo requirement.
- Sample order and target bulk quantity.
Related Products for Tap Drill Chart Buyers
Buyers using a helicoil tap drill chart usually also need matched inserts, STI taps, installation tools, repair kits, and size charts.
STI Taps
STI taps create the special installation thread required for wire thread insert installation.
Installation Tools
Installation tools, tang break tools, and extractor tools support wire insert repair kit workflows.
Thread Repair Kits
Repair kits combine inserts, drill bit, STI tap, installation tool, tang break tool, and case.
FAQ: Helicoil Tap Drill Chart
Is a helicoil tap drill chart different from a standard tap drill chart?
Yes. A standard tap drill chart is used for normal internal threads. A wire thread insert repair requires a drill size matched to the STI tap and insert system.
What does STI tap mean?
STI means Screw Thread Insert. An STI tap creates the installation thread that holds the wire insert after repair or reinforcement.
Can I use a standard tap for wire thread inserts?
No. A standard tap does not create the correct installation thread for wire thread inserts. Use the matching STI tap for the insert system.
What is the common M6 helicoil tap drill size?
For M6 × 1.0 wire thread insert repair, 6.3 mm is a common STI tap drill reference. Confirm final values by insert system, material, and repair condition.
What is the common M8 helicoil tap drill size?
For M8 × 1.25 wire thread insert repair, 8.3 mm is a common STI tap drill reference. Confirm the matching M8 × 1.25 STI tap and insert length before ordering.
Why do different helicoil STI drill charts sometimes show different numbers?
Published receiving-hole or drill recommendations can vary by insert system, STI tap data, tolerance, parent material and manufacturer guidance. Use a web chart for lookup and RFQ preparation, but use the approved insert/STI system for controlled production.
Why can M6 × 1.0 be shown with nearby drill values such as 6.2 mm or 6.3 mm?
Different insert and STI tap systems can publish nearby preparation values. This page uses 6.3 mm as a common M6 × 1.0 repair reference; do not override the selected system’s controlled data solely to match a generic chart.
Does this page also cover M2, M2.5, M16 and M20 wire insert sizes?
Yes. Those metric coarse sizes are included in the additional-size coverage section. Confirm the actual drill value from the selected insert/STI tap specification before machining or printing kit instructions.
Can Taiyi supply STI taps and complete repair kits?
Taiyi can review wire thread inserts, STI taps, drill bits, installation tools, tang break tools, refill packs, and private-label repair kits based on your size list and quantity.
Need STI Taps, Drill Sizes or Repair Kits?
Send your thread size, pitch, insert length, drill bit requirement, STI tap requirement, kit contents, packaging format, and order quantity. Taiyi can review inserts, taps, tools, refill packs, and private-label kits.