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Micrometer calibration in the UK

Updated: 22 October 2026

A spanner was in the case, the lines now meet, and it is tempting to write calibrated in the book. Micrometer calibration in the UK is two duties. At home you check zero for the session. In a laboratory that must show traceability, UKAS describes a path a spanner does not finish. Ordinary hand movements stay on [how to use an outside micrometer](/hub/measuring-and-marking-tools/outside-micrometer/sub/outside-micrometer-how-to-use). Listings are the [outside micrometer comparison](/hub/measuring-and-marking-tools/outside-micrometer). Peter F. used UKAS LAB 24, National Physical Laboratory guides and the amazon.co.uk listings on 20 October 2026. Nothing here was sent to a laboratory. A qualifying purchase can earn a commission at no extra cost to you.

A spanner was in the case, the lines now meet, and it is tempting to write calibrated in the book. Micrometer calibration in the UK is two duties. At home you check zero for the session.

Our top picks

Proster Proster PST185, 0–25 mm

Best overall

Proster Proster PST185, 0–25 mm
8.4/10about £14.95
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Proster Proster set, 0–100 mm

Alternative

Proster Proster set, 0–100 mm
8.4/10about £54.99
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GEU GEU, 0–25 mm

Preis-Tipp

GEU GEU, 0–25 mm
7.2/10about £9.99
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On this page
  1. 1.A zero check is not a calibration certificate
  2. 2.Which standard the range needs
  3. 3.What changes in a laboratory
  4. 4.Temperature and a tool that will not zero

A zero check is not a calibration certificate

The wrench moves the sleeve so a closed 0–25 mm micrometer reads zero. That shows the lines agree at one point today, after a clean. It does not state an uncertainty, and it does not check the screw or the faces along the travel. UKAS LAB 24 is for laboratories doing mechanical testing. It expects working micrometers on an annual external calibration, or a gauge-block check that includes anvil flatness and parallelism, and it allows a level 2 in-house method only with UKAS approval. That is not a Sunday brake-disc ritual. The current British standard for the instrument is BS EN ISO 3611:2023. BS 870:2008 is the older specification. You do not need either set of tables to see that a spanner is not a certificate. An inspection slip is the maker’s paper. Call it UKAS only if it says UKAS. None of these listings is described as shipping one. A calibration tool in a GEU review is what that buyer found in the box. Consumer Rights Act 2015 covers goods not as described. It is not a calibration interval.

Which standard the range needs

A 0–25 mm micrometer closes on its faces. Clean them, use the ratchet, and see if zero lines up. The spanner is the session adjustment. Many reviews of the £14.95 Proster describe that arrival. The adjustment does not prove the reading at 18 mm. A range above zero cannot be checked in fresh air. A 25–50 mm frame zeros on a 25 mm rod. A 50–75 mm frame needs a 50 mm rod. The Proster four-piece bullets name 25, 50 and 75 mm standards. The Tasofac bullets name five rods through 125 mm and no 150 mm rod. The Estink and Ejoyous listings name no matching rod. A review is not an included-components line. Do not borrow a metric rod and call an inch thimble zeroed. Which frame needs a rod is set out in the outside micrometer buying guide.
Proster Proster PST185, 0–25 mm

Testsieger

Proster Proster PST185, 0–25 mm
8.4/10about £14.95
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What changes in a laboratory

In a UKAS mechanical-testing laboratory, LAB 24 puts the micrometer on a traceable path: annual external calibration, or an approved gauge-block route, looking past the zero line to the travel and the faces. A level 2 check on site needs UKAS acceptance. A home workshop does not inherit that annual send-away as a statute. UKAS LAB 5 says a due date on a certificate is there because the customer asked for one. The paper does not invent a universal expiry. If nobody else’s specification depends on the number, a yearly visit is a choice. The session zero still stands. A brake-disc curiosity needs a clean close and a second reading. It does not need a courier. Two UK reviews of the £71.99 Neoteck refuse it for production or an ISO 9001 system because there is no certificate. The price did not change the duty. The use did.

Temperature and a tool that will not zero

Drawing sizes are at 20 °C. A collar just off the lathe, or a frame warmed in the fist, is not at that size. Let the work cool. Do not invent a correction you have not measured. Here the rule is a settled temperature and a reference of 20 °C. Stop when the spanner cannot zero a 0–25 mm tool, when the rod is missing on a longer frame, or when the faces do not meet. One TOPWAY review cites about 0.2 mm out of parallel. Moving the sleeve does not flatten those faces. One Ejoyous review keeps a known offset. That is a private workaround, not a calibration. When someone else will rely on the number, send the instrument to a competent laboratory. Do not write calibrated because the spanner was in the lid.

Common questions

Is the included wrench a calibration?
No. It moves the sleeve so a zero you can already touch lines up. It does not report an uncertainty or inspect the faces along the travel. LAB 24’s annual path is a laboratory duty. A review that says calibration tool is describing the box. Call a certificate UKAS only when the paper says UKAS.
How do I zero a 0–25 mm micrometer?
Clean the faces, close on the ratchet, and see whether both zeros agree. Use the spanner if they do not. Many buyers of the £14.95 Proster do that on arrival. If the adjustment runs out before the lines meet, stop. The reading sequence sits on the how-to page. This check is not a certificate.
How do I zero a 25–50 mm micrometer?
Close it on a 25 mm setting standard with the ratchet, and read zero there. The faces never meet, so fresh air is not a check. The Estink listing does not name a rod, so the standard has to come from you. A 50–75 mm tool needs a 50 mm rod in the same way. Winding the thimble shut does not create that bar.
Does a home workshop have to send it away every year?
No. The annual path is the laboratory context in LAB 24, and any workshop whose customers demand a certificate. LAB 5 says a printed due date is customer-requested, not an automatic expiry. A home shim or brake disc still needs a session zero. Send the tool when someone else’s specification depends on it, or when it will not zero and you still need the number.
What temperature matters?
20 °C is the reference for the drawing size. A hot part or a frame soaked in the hand is not at that size, even if the thimble looks decisive. Let the work cool. The effect is real on a caliper and on a micrometer. It is not a licence to apply a homemade correction.
What if the adjuster cannot reach zero?
Stop using the reading. A sleeve that will not meet, faces that stay apart, or a missing rod on a 25–50 mm tool means you do not have a size to pass on. Reading around a known offset, as one Ejoyous buyer did, is a hobby note, not a calibration. A competent laboratory is the next step when the number still has to be trusted.
Is a slip in the box a UKAS certificate?
Only if it says UKAS and names the checks. A maker’s slip, a plastic case, or the word calibration in a review is not that certificate. None of these listings is described as including one. BS EN ISO 3611:2023 is the product standard. Owning a tool is not a calibration of your particular frame.

Related pages

Best outside micrometer

Outside micrometer

Outside micrometer buying guide: range before brand

How to use an outside micrometer on a metric sleeve

Micrometer vs vernier caliper for one outside size

Sources

Public UK sources first, then the amazon.co.uk listings compared on this page. Shelf prices and scores were taken from the stored listings on 20 October 2026. This is not a laboratory test.

  1. BSI, BS EN ISO 3611:2023 (retrieved 20 October 2026)
  2. ISO 3611:2023 (retrieved 20 October 2026)
  3. UKAS LAB 24 (retrieved 20 October 2026)
  4. NPL mgpg79 (retrieved 20 October 2026)
  5. NPL mgpg40 (retrieved 20 October 2026)
  6. Mitutoyo UK, 193-111 (retrieved 20 October 2026)
  7. amazon.co.uk Outside Micrometres bestsellers (retrieved 20 October 2026)
  8. Consumer Rights Act 2015 (retrieved 20 October 2026)