Research / editorial guide. We reviewed KATO documentation on October 19, 2026. No insert was purchased, measured, installed, or strength-tested for this guide. As an Amazon Associate I earn from qualifying purchases. This guide has no Amazon product links. See our affiliate disclosure.
What the D means
D refers to the nominal diameter of the thread, not the outside diameter of the loose coil. In M8 × 1.25, the nominal diameter is 8 mm; 1.25 identifies the thread pitch. The pitch and the length multiplier are different fields.
KATO's March 2026 Design Manual lists the following values for its M8 × 1.25 row. The table's metric dimensions are in millimeters. We have paired those entries with three part numbers from its metric-coarse, non-locking, tangless column.
| Nominal-length label | Nominal catalog length | KATO tangless, non-locking catalog example |
|---|---|---|
| 1D | 8.0 mm | 2TNM-8X1.25C-8 |
| 1.5D | 12.0 mm | 2TNM-8X1.25C-12 |
| 2D | 16.0 mm | 2TNM-8X1.25C-16 |
Sources: KATO Design Manual, printed pages 20–21 for the dimension headings, definition, and units; printed page 37 for these exact part numbers. The arithmetic is 1, 1.5, or 2 multiplied by 8 mm. It describes the catalog's nominal-length labels.
These are documentation examples, not a recommendation to buy one length or a claim of current stock. Keep the full designation from the actual offer, including any finish or packaging information. KATO explains its part-number fields on printed page 19. Do not transfer this table to another brand, a locking series, or an M8 thread with a different pitch.
Separate nominal, free-state, and installed length
Three descriptions can appear around the same product:
| Description | What you are reading or observing | How to use it here |
|---|---|---|
| Nominal length | The manufacturer's calculated catalog designation | Match the label to the exact part-number row and its definition |
| Free-state length | The physical length of the loose, uninstalled coil | Keep an observation separate from the nominal label; it is not a substitute for the specified identification procedure |
| Installed length | The coil's length in the receiving thread | Obtain the applicable drawing or instructions; do not relabel the nominal entry as this dimension |
KATO's nominal-length explanation describes a loose coil as wider and shorter than it is after installation: reducing its diameter in the receiving thread makes it longer. That change explains why a ruler reading on a loose insert and a catalog length designation are different kinds of information.
The manual's page 20 footnote defines KATO nominal length as installed length plus half a thread pitch. We include that definition to explain the column heading, not to calculate installation dimensions. A nominal 12 mm entry should not be copied into a worksheet as a measured free-state length, an actual installed length, or a required drilling depth.
Compare the order before changing the length
Start with the package label, supplier quotation, and applicable manufacturer document. Do not begin by stretching a loose coil until it matches a number in a listing.
- Match the complete thread. Record M8 × 1.25 rather than only M8.
- Match the insert design and series. Keep tanged or tangless, locking or non-locking, and the manufacturer's full part number together. Our examples use one specific column.
- Match the length label and its definition. Ask whether a stated millimeter value is nominal, free-state, or installed length. A bare “12 mm long” description leaves that question unanswered.
- Compare the offer with the received paperwork. Preserve the order, package designation, and document revision so a mismatch can be explained to the supplier.
For example, a quotation naming 2TNM-8X1.25C-12 and a package naming 2TNM-8X1.25C-8 point to different nominal-length rows in this catalog. Ask the supplier to resolve that mismatch. This comparison does not establish the identity or conformity of the physical contents.
If the package and quotation agree but a loose-part measurement worries you, ask for the applicable inspection method and acceptance requirements. If the insert is unmarked or its source is unknown, keep its identity unresolved. This guide provides no free-coil counting procedure or acceptance limits for loose inserts.
Keep a short supplier record
| Field | Record before accepting an unexplained substitution |
|---|---|
| Manufacturer and complete part number | The offer, package marking, and any difference between them |
| Thread and insert series | Complete size and pitch; tanged/tangless; locking/non-locking |
| Length information | D multiplier, millimeter value if supplied, and what state that value describes |
| Supporting document | Title, revision, applicable row or drawing, and supplier clarification |
| Unresolved observation | What differs, how it was observed, and the inspection information still needed |
You can adapt this inquiry:
My order specifies [manufacturer and full part number], [complete thread], and [nominal-length label]. The package or listing states [exact wording]. Please confirm which part is being supplied, whether the stated length is nominal, free-state, or installed length, and the applicable document and inspection method. Please resolve [specific mismatch] before substituting another length.
The record and inquiry are editorial tools for finding missing information. They are not a material inspection certificate or permission to install the part.
What the label cannot choose for you
A longer label alone does not establish greater repair strength or suitability. Required engagement, material, available geometry, tool clearance, and the equipment's approved repair procedure remain separate questions. Do not replace a specified length merely because another coil looks easier to fit.
For a closed-end hole, use the blind-hole M8 planning worksheet. For the driver and tang-handling decision, use the tanged versus tangless checklist. If you are still comparing repair systems, return to the M8 coil versus solid insert guide.
For safety-critical components, use the equipment manufacturer's approved repair information and qualified help. This catalog comparison supplies no torque, drilling depth, minimum wall thickness, or strength rating.
Sources and limits
- KATO Design Manual, March 2026: printed page 19's part-number fields, pages 20–21's nominal-length definition and metric dimensions, and page 37's exact non-locking M8 × 1.25 catalog examples.
- KATO: Nominal Length: the change from free state to installed state. This guide does not reproduce its coil-identification or material-thickness procedures.
These sources describe KATO's system. They do not establish another manufacturer's length convention, cross-brand interchangeability, the identity of an unmarked insert, or suitability for your component. The order checks and supplier inquiry are editorial judgments. No product testing or generated technical illustration supports this guide.