Before buying, confirm the complete thread designation, the usable hole geometry, and the exact repair system's preparation requirements. If the instructions do not explain how that system fits your blind hole, keep it off the purchase list until the manufacturer or a qualified machinist can resolve the gap.
This guide is a planning worksheet for non-safety-critical metal workbench parts. It does not approve a repair, prescribe a drilling depth, or replace an equipment maker's repair procedure. For vehicle, lifting, structural, pressure-containing, or other safety-critical joints, use the equipment maker's approved information and qualified help.
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01 / Four measurements
Keep four different measurements separate
A depth reading and an insert length do not describe the same thing. Make a separate entry for each item below.
| What you need to know | What it tells you | What it does not establish |
|---|---|---|
| Existing hole geometry and depth | Where the hole ends relative to the chosen reference surface | How much of that space has usable, complete threads |
| Required full thread depth | How much correctly formed receiving thread the insert system needs | The total drilling depth or the tap's required travel |
| Insert length and installed position | Which exact insert is being considered and where it must sit | Whether the tap, driver, or tang tool has clearance |
| Tool travel and clearance | Whether each specified tool can complete its job without hitting the bottom | Whether the repaired joint has adequate strength |
Record where a depth measurement starts and ends, plus the measuring method. A reading taken to the deepest point is not automatically a measurement of usable threaded depth. If damage or access makes the geometry uncertain, mark it unknown instead of rounding it into a kit specification.
This separation is our editorial checklist. It follows the distinctions in the manufacturer references below; it is not a clearance formula.
02 / Read the catalog
Read the column heading before using the number
E-Z LOK's catalog provides a useful example. In its metric-internal/metric-external carbon-steel table, part 450-8 has an M8 × 1.25 internal thread, a listed 12.5 mm insert length, and 14.5 mm minimum full thread depth. Those last two entries have different labels and different purposes. E-Z LOK catalog, PDF page 3, printed page 5
The 14.5 mm entry is not a drilling-depth instruction. This example does not establish that a particular 14.5 mm-deep blind hole can accept that insert. It also does not establish adequate surrounding material or tool clearance.
Use the row for the exact insert part number and keep the original units and column headings in your notes. When a dimension is missing, ask for the application drawing or installation instructions. Do not substitute the dimensions of another M8 insert.
03 / Tool clearance
Check the tools as well as the insert
TIME-SERT's blind-hole guidance explains why extra space can be needed: the tap has a lead before it produces full threads, and its installation driver must pass through the insert's lower threads to perform that system's locking operation. The manufacturer also warns against bottoming the driver. TIME-SERT FAQ, question 5
That explanation applies to the described TIME-SERT process. Do not transfer its clearance allowance or locking procedure to E-Z LOK, a wire-coil kit, or an unverified marketplace kit.
For a coil system, confirm the exact tap and installation tooling. E-Z LOK identifies 40870 as an M8-1.25 STI tap, but its documents differ: the product page calls it Bottoming, while the metric-coarse catalog table, PDF page 7, printed page 13 lists it under STI Tap (Intermediate). We have not resolved that difference. Ask the manufacturer to confirm the current tool’s lead—the entry section before full cutting threads—and required travel for your hole. Neither label establishes clearance. STI means screw thread insert; the tap prepares the receiving thread for the insert. This is a documentation example, not a tool recommendation.
Before ordering, get answers to these questions:
- Which exact tap and driver does the chosen insert require?
- What preparation depth and complete thread depth does the manufacturer specify?
- Is the listed tap suitable for this blind-hole geometry?
- Does any tool need to travel beyond the installed insert?
- Can the tools reach the hole on the required axis, with room to operate and withdraw?
If a kit description supplies only a thread size and a tool count, the blind-hole fit question is still open.
04 / Chips and tang
Plan for chips and any tang
A tang is the small drive feature on some wire-coil inserts. E-Z LOK's tanged-coil instructions include a tang-break tool and a tang-removal step. Do not assume every coil system has the same tooling or removal procedure. E-Z Coil installation instructions
For a blind hole, our planning recommendation is to ask how you will remove and account for machining chips and any detached tang using the assembly's approved cleaning procedure. Include inspection access in that question. A hole that accepts the insert but cannot be checked afterward is not a completed plan.
Do not improvise by driving debris deeper into the hole or by forcing a fastener through an obstruction. If a loose fragment could enter an inaccessible cavity, stop and resolve the cleaning and inspection method before cutting.
05 / Stop conditions
Do not solve missing clearance by guessing
A shorter insert, a shorter bolt, or a deeper hole each changes a different part of the repair. None is an automatic answer to a fit problem.
TIME-SERT's FAQ 17 warns against simply cutting its inserts shorter: their upper and lower features serve installation and locking functions. The same FAQ discusses a special short-hole situation separately in question 22. Treat an unusual short hole as a reason to obtain guidance for the exact part from the manufacturer, not as permission to improvise that procedure. TIME-SERT FAQ, questions 17 and 22
Thread engagement also needs its own assessment. Bossard's guidance explains that required engagement depends on the component material's strength. Merely fitting inside a hole does not establish a joint's load capacity. Bossard: thread engagement length
Leave drilling depth, remaining wall, required engagement, and tightening specifications to the exact repair and equipment documentation. A generic “M8” label cannot supply those limits.
06 / Buying worksheet
Fill in this worksheet before ordering
Use a sketch or notes for one real part. Keep measured observations separate from manufacturer requirements.
| Field | Record this |
|---|---|
| Part and use | Part identity, material if known, purpose, and whether the joint is safety-critical |
| Original thread | Complete designation and the documentation or identification method supporting it |
| Existing condition | Damage, previous repairs, visible cracks, and anything you cannot inspect |
| Geometry | Reference surface, depth measurement and method, nearby edges or cavities, and unknowns |
| Proposed system | Manufacturer, kit number, insert part number, length, and exact instructions |
| Preparation | Specified receiving thread, full thread depth, hole preparation, and tool clearance |
| Access and cleanup | Tool access, chip removal, tang handling if applicable, and inspection method |
| Completed joint | Required engagement, fastener specification, and approved tightening procedure |
Ready to compare kits: the original thread is confirmed, the proposed system's instructions address the hole and material, and the remaining requirements have documented answers.
Not ready to buy: a required dimension, tool, inspection method, or application approval is unknown. Keep that item open; do not treat the missing answer as permission to proceed.
For a supplier inquiry, adapt this short template:
I am evaluating [exact insert and kit] for a blind hole in [part and material]. The original thread is [complete designation]. My sketch shows the reference surface, existing depth and measuring method, nearby material, and tool access. Please confirm the applicable installation drawing, required full thread depth, hole preparation depth, tool travel, and cleanup or tang-removal requirements. Which additional information do you need before confirming suitability?
This template helps obtain missing information. A supplier's product answer does not replace the equipment maker's approval where one is required.
07 / Related guides
Where to go next
- If the original thread is uncertain, start with metric vs SAE thread identification.
- If you have not decided whether an insert is appropriate, use the stripped-thread repair decision guide.
- Once the geometry and instructions are resolved, the M8 coil vs solid insert guide covers system differences and kit-content checks.
- For driver and tang-handling purchasing questions, use the tanged vs tangless tooling checklist.
08 / Evidence and limits
Evidence and limits
Prepared from manufacturer documentation checked September 18 and rechecked September 29, 2026. We have not installed or strength-tested these systems for this guide. The worksheet, stop conditions, and inquiry template are editorial synthesis. The catalog example explains labels; it is not an installation specification for a reader's part.