Description
Product Overview
The Mitutoyo 139-173 is a tubular inside micrometer set covering 100–500mm — a serious range that puts large-bore measurement squarely within reach without reaching for a dedicated bore gauge or stacking extension rods past the point of reliability. Designed for direct inside diameter measurement of bores, housings, cylinders, and large-diameter features, this set uses a modular rod-and-head system that lets you swap measuring lengths quickly on the bench. If you’re sizing up large spindle bores, hydraulic cylinder IDs, gearbox housings, or setting up a large four-jaw job, this is the tool that earns its place in the toolroom cabinet.
- 100–500mm measuring range across the set — the jump from 100mm up to 500mm is handled by swapping interchangeable extension tubes, keeping each measurement mechanically direct and avoiding the accumulated stack-up error you’d get from chaining multiple short-range instruments together. That matters when you’re chasing bore tolerances in the tens of microns.
- Tubular micrometer construction — unlike a telescoping gauge that requires a follow-up measurement on an outside mic, this instrument reads directly on its thimble. You get your number at the bore, no secondary transfer step, no additional measurement uncertainty introduced by hand feel.
- Mitutoyo ground and lapped measuring faces — the contact points are hardened and precision-ground to Mitutoyo’s toolroom standards, maintaining flat, parallel contact across the bore and giving repeatable seating with each measurement. On a large-bore application, that consistent seating is what separates a credible reading from a guess.
- Modular extension rod system — the set ships with multiple extension tubes (visible in the case cutouts) to step through the measuring range. The head unit with thimble is common across all extensions, so you’re reading off a single calibrated instrument regardless of which tube is fitted. A spanner/pin wrench for assembly is included in the case.
- Ideal for — measuring large hydraulic and pneumatic cylinder bores, sizing gearbox and transmission housings, checking large lathe chuck backplate register bores, verifying large bearing housing IDs, and confirming bore diameters prior to interference or transition fit assembly on shafts in the 100–500mm range.
Condition
Used (Good Condition / Previously Used, Fully Functional)
The set presents well for a used instrument of this class. The chrome and satin-finish barrel surfaces on the head unit show the expected light shop patina — minor handling marks and the kind of superficial wear you’d see on any tool that’s done real work — but nothing that suggests abuse or careless storage. The knurled thimble and barrel show no significant dings, the thimble rotates smoothly with no detectable roughness or binding through the full travel, and the locking mechanism functions correctly. The measuring faces across the contact points appear clean and free from pitting or damage that would affect seating. The extension tubes seat firmly without detectable slop in their joints, which is where these instruments can develop problems if they’ve been mishandled — these look solid. The original Mitutoyo case is present and the foam insert is intact with all positions occupied, including what appears to be the original pin wrench. As with any used precision instrument of this range, verification against a known ring gauge or calibrated bore standard at your working size is strongly recommended before putting the set to work on close-tolerance jobs. A wipe-down with instrument oil on the threads and measuring surfaces before first use is good practice.
Included
- 1 x Mitutoyo 139-173 Tubular Inside Micrometer Set, 100–500mm
- 1 x Micrometer head / thimble unit
- Multiple interchangeable extension tubes (spanning 100–500mm range)
- 1 x Pin wrench / spanner for tube assembly
- 1 x Original Mitutoyo fitted carry case with foam insert
Not Included
- Calibration certificate (not included — independent recalibration recommended for critical tolerance work)
- Setting ring gauge (not included — required if formal zero verification is needed)
Brand Information
Mitutoyo Corporation is Japan’s largest manufacturer of precision measuring instruments and is widely regarded as the global benchmark in metrology tooling — sitting at the top tier alongside Mahr, Tesa, and Starrett. Founded in 1934 in Kawasaki, Japan, Mitutoyo has built its reputation on consistent manufacturing tolerances, traceable calibration standards, and instruments that hold their accuracy across decades of shop use. In the Australian machining and toolmaking trade, Mitutoyo is considered the default choice for toolroom-grade work, and their instruments routinely appear in quality-critical environments from aerospace and defence subcontracting through to precision job shops and TAFE training centres.
Specifications
| Feature | Specification |
|---|---|
| Brand | Mitutoyo |
| Model / Series | 139-173 |
| Type | Tubular Inside Micrometer Set |
| Measuring Range | 100–500mm |
| Graduation / Resolution | 0.01mm |
| Accuracy | ±0.006mm (refer to Mitutoyo 139-series specifications — verify against current datasheet for confirmation) |
| Construction | Hardened and ground measuring faces; tubular stainless / chrome-plated steel extension rods |
| Extension System | Interchangeable tubular extension rods |
| Country of Origin | Japan |
| Condition | Used — Good Condition |
| Included Items | Micrometer head, extension tubes (full set for 100–500mm range), pin wrench, original fitted case |
| Not Included | Calibration certificate, setting ring gauge |
Keywords
Mitutoyo 139-173, Mitutoyo tubular inside micrometer, inside micrometer set 100-500mm, bore mic large diameter, tubular micrometer set, Mitutoyo bore measuring, large bore inside micrometer, toolroom micrometer Australia, inside mic set metric, hydraulic cylinder bore measurement, gearbox housing measurement, precision bore gauge Australia
