Description
Product Overview
The Mitutoyo Holtest 368-902 is a three-point internal micrometer covering the 12–20mm bore range — the go-to instrument when you need to measure a bore diameter with the kind of repeatability and centreline accuracy that a two-point bore gauge or snap gauge simply can’t match. Unlike a two-point instrument, the Holtest self-centres automatically via its three equally-spaced contact anvils, eliminating the rocking error that plagues traditional internal mics. For toolroom and production work where bore tolerances are measured in tenths, that self-centreing geometry is everything.
- Three-point self-centreing contact system — The three carbide-tipped anvils make simultaneous contact at 120° spacing, finding the true bore centreline automatically. This means you’re always measuring the actual diameter, not a chord — critical when chasing close tolerances on bushes, bearings, hydraulic bores, or precision fits.
- 0.001mm graduation — One-micron resolution gives you the granularity needed for H7/h6 fits and similar close-tolerance work. Reading in thou, that’s roughly 0.00004″ per graduation — enough resolution to confidently sort a press fit from a running fit without ambiguity at the thimble.
- 12–20mm measuring range with interchangeable extensions — The 368 series uses a modular extension rod system, so the same micrometer head covers the full 12–20mm span. This keeps the tool compact in the bore without the bulk of larger instruments, and the extension system means you’re not buying multiple heads to cover adjacent ranges.
- Calibration / zeroing via setting ring — Unlike a standard outside micrometer with a flat anvil zero, the Holtest must be set against a precision ground reference ring at each measurement range. The setting ring is included in this lot, which is non-trivial — Mitutoyo rings are ground to ±0.001mm and cost real money to source separately.
- Ideal for — Checking bore diameters on bearing housings, bushes, and hydraulic cylinder bores; verifying reamed or line-bored holes to drawing tolerance; measuring lathe chuck jaw bores; production inspection of small bores on machining centres and CNC lathes; toolroom inspection of ground bores and press-fit housings.
Condition
(Used — Good Condition / Previously Used, Mechanically Sound)
The instrument is in good used condition. The thimble rotates smoothly with no perceptible backlash, and the anvils extend and retract freely with consistent feel — there are no signs of internal wear or binding that would affect measurement repeatability. The carbide anvil tips show normal service wear but no chipping or deep scoring that would compromise contact geometry. The barrel graduations and thimble scale are clean and fully legible. The outer barrel shows light handling marks and minor surface patina consistent with workshop use, but the precision ground measuring surfaces are intact. The setting ring shows no damage to its bore or reference face — it presents as a usable calibration reference. As with any used precision instrument, best practice before putting this to work is to set it against the supplied ring gauge, verify the zero at the midpoint of the range, and confirm repeatability with three consecutive readings before trusting it on critical work. If you’re using it for formal inspection, a NATA-traceable recalibration is advisable; for toolroom and production floor use, verification against the setting ring is the standard procedure and should be entirely sufficient.
Included:
- 1 x Mitutoyo Holtest Three-Point Internal Micrometer, 12–20mm, 0.001mm graduation (Series 368, Model 368-902)
- 1 x Mitutoyo original fitted carry case
- 1 x Setting / reference ring gauge (Mitutoyo, appropriate to range)
- 1 x Extension rod(s) for range coverage
- 1 x Mitutoyo certificate / warranty papers (保証書)
- Original plastic protective sleeves / packaging inserts
Not Included:
- No separate calibration certificate from a NATA-accredited laboratory — recalibration recommended if formal traceability is required
Brand Information
Mitutoyo Corporation, founded in Japan in 1934, is the world’s largest manufacturer of precision measuring instruments and the benchmark against which most other metrology brands are judged. Their instruments are manufactured to exacting tolerances in Japan under rigorous ISO 9001-aligned quality systems, and Mitutoyo sits firmly at the top tier of the global metrology market — alongside Mahr and Tesa for hand-held instruments, and well above the bulk of Chinese and Taiwanese production tooling. In Australian toolrooms, Mitutoyo is the de facto standard: if a drawing calls for a calibrated measurement, chances are it’s being taken with a Mitutoyo.
Specifications
| Feature | Specification |
|---|---|
| Brand | Mitutoyo |
| Model | 368-902 |
| Type | Three-Point Internal Micrometer (Holtest) |
| Series | 368 |
| Measuring Range | 12–20mm |
| Graduation / Resolution | 0.001mm (1 micron) |
| Accuracy | ±0.003mm (per Mitutoyo specification for this series) |
| Contact Points | 3 x carbide-tipped anvils, self-centreing at 120° spacing |
| Material / Construction | Hardened steel body, carbide anvil contacts |
| Zeroing / Calibration Method | Setting ring gauge (included) |
| Extension System | Interchangeable extension rods (included) |
| Country of Origin | Japan |
| Condition | Used — Good Condition |
| Included Items | Instrument, original case, setting ring, extension rod(s), warranty/certificate papers, original packaging inserts |
| Not Included | NATA-traceable calibration certificate |
Keywords
Mitutoyo 368-902, Mitutoyo Holtest, Mitutoyo three-point internal micrometer, bore mic 12-20mm, internal micrometer 12mm 20mm, Holtest bore gauge, three-point bore micrometer, small bore measurement toolroom, precision bore gauge Australia, internal mic with setting ring, Mitutoyo 368 series, bore micrometer machining centre
