Dimensional Measurement · Micrometers
Outside Micrometer
Outside micrometers in two grades: digital styles reading to 0.001 mm, and mechanical styles from 0-25 to 225-250 mm, both with carbide measuring faces and a ratchet stop.
Key specifications
- Resolution
- 0.001 mm digital / 0.01 mm mechanical
- Tolerance
- ±0.002 mm digital / ±0.02 mm mechanical
- Digital ranges
- 0-25, 25-50, 50-75, 75-100 mm
- Mechanical ranges
- 0-25 to 225-250 mm, in 25 mm steps
- Measuring faces
- Carbide
- Measuring force
- Ratchet stop
- Frame
- Precision-cast stainless steel, coated
- Reading
- LCD with SET and ABS keys (digital), laser-engraved thimble (mechanical)
- Sealing
- IP65 on the sealed digital style, 0-25 mm
An outside micrometer measures the outside diameter of a part, or the wall thickness of tube where a wall-thickness anvil is fitted, and reads it straight off the instrument. Each instrument covers a 25 mm window, so a workshop holds a set rather than one tool: a small frame for pins and shafts, a larger one for bigger work.
The instruments on this page come in two grades. The digital grade resolves to 0.001 mm and is stated to hold ±0.002 mm, showing the figure on an LCD with zero-and-preset and absolute-to-relative keys. The mechanical grade resolves to 0.01 mm and is stated to hold ±0.02 mm, read from a laser-engraved thimble and sleeve. The grades are not interchangeable where a drawing tolerance sits near what the mechanical instrument can hold.
Both grades share the same construction: a precision-cast frame with an electrostatic coating, carbide measuring faces, a ratchet stop that fixes the measuring force, and a mechanical spindle lock so a reading can be held while it is recorded.
How an outside micrometer works
The part is held between a fixed anvil and a spindle, and the spindle is advanced by a calibrated screw. Because the screw moves the spindle a fixed distance per turn, the reading is a length in its own right rather than a comparison against a separate gauge — which is why the instrument is used on its own, without a reference part.
The measuring force is the difference between a dependable reading and a repeatable-looking wrong one. The spindle is advanced through a ratchet stop, which slips once a set force is reached, so the faces meet the part the same way each time. A reading taken by winding the thimble in by hand depends on how tightly it was closed, and on a soft or thin-walled part the difference exceeds the tolerance of the instrument itself.
On the digital styles the spindle position is read electronically inside the head and the value is shown on the display, so there is no scale to interpret. That is faster, and it is also why the digital styles carry the finer stated tolerance. The mechanical styles put the same measurement on a graduated thimble, and need no power at all.
How to select the right outside micrometer
Work outwards from the drawing. The tolerance at the dimension being measured decides the grade: if the drawing allows more than the mechanical instrument is stated to hold, the mechanical grade is adequate and the money is better spent on the sizes needed. If it allows less, the digital grade is the one that can demonstrate the figure.
Then settle the range. The largest dimension in the batch decides which size of instrument is bought, and the material or the surface finish may decide whether a lighter touch is needed — which the ratchet stop provides on every instrument here rather than on some of them.
Then consider where the instrument will live. Dust, swarf and coolant splash are what the sealed digital style exists for, and the drawing offers it in one range only, so if the environment is dirty and the parts are large, that has to be raised in the enquiry rather than assumed. If tube wall is measured as well as outside diameter, the wall-thickness anvil is what makes the same instrument do both jobs.
Send the dimension, the size band, the drawing tolerance and the environment, and the grade and range follow from them.
Measurement limitations and selection considerations
An outside micrometer measures outside dimensions. An inside diameter, a bore, a depth or a step needs a different instrument — an inside micrometer, a bore gauge, a dial indicator or a caliper — and no frame size or accessory converts one into the other.
The 25 mm window is the second limit. Measuring a batch that spans a wider size band means either several instruments or a different tool, and a dimension that sits at the very bottom of an instrument’s travel is better measured on the smaller instrument that has it in the middle of its range.
Carbide faces are hard but they are not indestructible. Measuring a rotating part, a casting skin or an abrasive material wears the faces, and worn faces are the usual reason a micrometer that once agreed with a gauge block starts to disagree.
Two statements in the supplied material are incomplete and worth knowing before a tolerance is promised. The deviation is given as three values without a range attached to each, so for the mechanical grade we cannot say which figure applies to which size. And the sealed style is offered in a single range, so a dirty environment combined with large parts is a case to confirm rather than assume.
The material also describes the two grades as national-standard and industrial grades without naming the standard they refer to. The tolerance figures on this page are therefore the whole of the accuracy statement we can publish; where an application calls for a particular standard to be cited, tell us and we will confirm what documentation can be supplied with the instrument.
Before use, the two measuring faces and the setting rod should be wiped clean and the instrument zeroed against the rod on ranges above 0-25 mm. Checking zero is what catches the case where a setting rod has been dropped or a face has picked up a burr.
Features
- Carbide measuring faces, chosen for wear resistance when the same dimension is measured repeatedly
- A ratchet stop that fixes the measuring force, so repeated readings on the same part agree
- Laser-engraved graduations on the mechanical scale
- Digital styles showing 0.001 mm, with SET zero and preset and ABS absolute-to-relative switching
- A sealed digital style rated IP65 for dusty benches and coolant splash
- Setting rods supplied above the 0-25 mm range, so zero can be checked on the instrument as it is used
- A wall-thickness anvil supplied with the digital styles, so tube wall can be measured without a second instrument
- A mechanical spindle lock, so a reading can be held while it is written down
Technical specifications
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
| Resolution, digital styles | 0.001 mmStandard |
|---|---|
| Tolerance, digital styles | ±0.002 mmStandard |
| Resolution, mechanical styles | 0.01 mmStandard |
| Tolerance, mechanical styles | ±0.02 mmStandard |
| Digital measuring ranges | 0-25, 25-50, 50-75, 75-100 mmStandard |
| Mechanical measuring ranges | 0-25 to 225-250 mm, ten ranges in 25 mm stepsStandard |
| Reading, digital styles | LCD, displays to the 0.000 mm position, SET zero and ABS mode keysStandard |
| Reading, mechanical styles | Thimble and sleeve, laser-engraved graduationsStandard |
| Stated deviation, mechanical styles | 4 / 5 / 6 µm, not tied to a range in the drawingInformation required |
| Accuracy reference standard | Information requiredInformation required |
| Measuring faces | CarbideStandard |
|---|---|
| Frame | Precision-cast, electrostatically coated, reinforced housingStandard |
| Body material | Stainless steelStandard |
| Measuring force device | Ratchet stopStandard |
| Spindle lock | Mechanical lock, so a reading can be held while it is recordedStandard |
| Setting rod | Supplied with ranges above 0-25 mm, for zero checkingStandard |
| Wall-thickness anvil | Supplied with the digital stylesStandard |
| Stand | Offered with one digital variant; the drawing does not describe it furtherOptional |
| Display supply | Battery, supplied with the precision digital style; type not statedInformation required |
|---|---|
| Sealing on the sealed style | IP65, dust class 6 and water class 5, 0-25 mm onlyOptional |
| Sealing on the other styles | Information requiredInformation required |
| Operating temperature | Information requiredInformation required |
Available models
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| 0-25 to 75-100 mm | Digital, standard style | 0.001 mm resolution, ±0.002 mm | Four sizes; wall-thickness anvil and case opener supplied |
| 0-25 mm | Digital, standard style, with stand | 0.001 mm resolution, ±0.002 mm | Stand form not described in the drawing |
| 0-25 mm | Digital, sealed style | 0.001 mm resolution, ±0.002 mm, IP65 | Offered in this range only |
| 0-25 to 75-100 mm | Digital, precision style | 0.001 mm resolution, ±0.002 mm | Four sizes; battery and spanner supplied |
| 0-25 to 225-250 mm | Mechanical | 0.01 mm resolution, ±0.02 mm | Ten sizes in 25 mm steps; setting rod supplied above 0-25 mm |
Certification and compliance
Certification documents not yet supplied
Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.
Parameters still to be confirmed
The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:
- Official model designations for each grade, style and range
- Accuracy reference standard behind the stated resolution and tolerance
- Deviation corresponding to each measuring range (the drawing gives 4 / 5 / 6 µm without tying a value to a range)
- Ingress protection of the sealed style (the drawing shows both IP65 and IP64)
- Whether styles other than the 0-25 mm sealed variant are offered sealed
- Battery type and life for the digital styles
- Operating temperature range
- Certification list and availability of certificate copies
- Warranty period and the terms that apply
- English-language datasheet and manual in PDF form
- Packaging dimensions and gross weight for freight calculation
Frequently asked questions
Which size range should be ordered for a batch of parts?
An outside micrometer measures over a 25 mm window, so the range has to bracket the largest dimension in the batch rather than the nominal one. A 0-25 mm instrument will not reach a 30 mm shaft, and a 25-50 mm instrument cannot be trusted at the bottom of its travel. Where a batch spans more than one window, tell us the smallest and largest dimension and we will quote the set of sizes that covers it. Ranges above 0-25 mm arrive with a setting rod, which is used to check zero before the instrument is trusted.
The display resolves to 0.001 mm — does that mean the reading is accurate to 0.001 mm?
No, and the two figures should be read together. Resolution is the last digit the display can show; the tolerance is what the instrument is stated to hold over its range. On the digital styles the tolerance is ±0.002 mm, which is the figure that matters when a drawing tolerance has to be demonstrated. The mechanical styles resolve to 0.01 mm with a ±0.02 mm tolerance, so a job that needs the finer figure needs the digital grade.
Digital or mechanical for a workshop that measures to a drawing?
It depends on the tightest tolerance on the drawing and on how the instrument is looked after. The digital grade carries the finer tolerance and reads faster, which matters where many parts are checked in a shift, but it depends on a battery and the sealed version is offered in one range only. The mechanical grade needs no power, covers sizes up to 225-250 mm, and is unaffected by being left in a drawer, but its tolerance is ten times the coarser figure. Many workshops hold both and use the mechanical instrument for the dimensions that are not near a limit.
Will it measure the wall thickness of a tube?
Yes, on the digital styles, which are supplied with a wall-thickness anvil for that purpose. Without it, an outside micrometer measures the outside span of the tube, which includes the wall on both sides. Tell us whether tube wall is being measured, so the anvil is quoted with the instrument rather than added later.
Can the sealed style be supplied in the larger ranges?
The drawing shows the sealed style, rated IP65 for dust and water spray, in the 0-25 mm range only. Whether the larger sizes are available sealed is not stated in the material supplied to us, so we have left the question open rather than assume it. Where the instrument is used at a machine with coolant, say so in the enquiry and we will confirm what can be supplied for the sizes you need.
What should be sent with an enquiry?
The dimension being measured, the smallest and largest size in the batch, and the drawing tolerance at that dimension, since those three settle the grade and the range. Add the material and surface of the part, whether it deforms under light pressure, the environment the instrument is used in, and whether a calibration certificate has to come with it. Quantity, destination port and required date let us answer with a quotation rather than a question.
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Send the configuration you need and we will confirm availability, lead time and terms. Minimum order quantity is 1 pc.
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Request a quotation - Outside Micrometer
Send the technical detail and we will confirm availability, lead time and terms. In-stock items ship within 48 hours; customized specifications typically take 2-10 days. Minimum order quantity is 1 pc.