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Gage blocks - Gauge blocks

NIST Certified gage blocks for calibration of micrometers, indicators, calipers etc.

Each rectangular steel or ceramic gage block comes with a serial number engraved and a certificate of accuracy traceable to NIST. These have a tolerance grade ASME 0, ideally suited for shop calibration as well as the inspection room.

They can be wrung together to create a larger span, 6" for calibrating a caliper, for instance. In fact, you can take any combination of blocks and put them end-to-end to create your desired length. For example, combining a 25 mm block with a 30 mm block will result in the equivalent of a 55 mm block.

A word of warning: it can be very tricky to handle more than two blocks at a time, so think carefully about which blocks you need to buy.

For ISO purposes, keep track of these serial numbers and keep a copy of the certificate with your calibration records. When you calibrate your instrument make note of the instrument's serial number and the serial numbers of the gage blocks which you used to calibrate it. Additionally, have the gage blocks certified by a local calibration lab on an annual basis and then keep the current certificate of calibration with your records.

These gage blocks are ideal for any micrometer or dial indicator having up to .0001" discrimination. If you don't need that kind of accuracy, consider getting a complete gage block set shown further down this page.

Instead of buying individual blocks for micrometer calibration you may want to look at the Micrometer Calibration Set on page 7.


1" rectangular steel gage block shown with an Etalon indicating micrometer.

Rectangular Gage Blocks — NIST certified — Grade 0
Thickness (steel) Accuracy Order No. Internet Pricing US$
.005"(see note) ± .000006" 611305-531 check price and stock
.010" ± .000006" 611310-531 check price and stock
.020" ± .000006" 611320-531 check price and stock
.025" ± .000006" 611325-531 check price and stock
.05" ± .000006" 611105-531 check price and stock
.0625" (1/16") ± .000005" 611303-531 check price and stock
.1" ± .000005" 611191-531 check price and stock
.125" ± .000005" 611165-531 check price and stock
.2" ± .000005" 611192-531 check price and stock
.25" ± .000005" 611212-531 check price and stock
.3" ± .000005" 611193-531 check price and stock
.4" ± .000005" 611194-531 check price and stock
.5" ± .000006" 611195-531 check price and stock
.75" ± .000006" 611217-531 check price and stock
1" ± .000006" 611201-531 check price and stock
1" (Grade 00) ± .000003" 611201-521 check price and stock
2" ± .000008" 611202-531 check price and stock
3" ± .000010" 611203-531 check price and stock
4" (see notes) ± .000012" 611204-531 check price and stock
5" (see notes) ± .000016" 611205-531 check price and stock
6" (see notes) ± .000016" 611206-531 check price and stock


All gage blocks above have these uniform dimensions:

  • width = .354"
  • height = 1.181"

Gage block source: these professional grade blocks are produced by Mitutoyo of Japan.

Note: The .005" block is well suited for calibration of paper and film thickness gages. It will be necessary to handle this gage block with extreme care because of its thickness (or lack thereof).

Note: if used for caliper calibration then a measuring rod may be more suitable for ranges longer than 4 inches. See page 58

What is the difference between the various grades?

The gauge blocks offered above have tolerances which have the broadest range of use suitable for the inspection room as well as for shop set-ups. The tolerances which we show are the deviation of length at any point from nominal length. For a 1-inch gage block with ±.000006" tolerance, this means that at any point the gauge block may be as long as 1.000006" or as short as .999994". For all practical purposes, this is as close to 1" as you're likely to want to get.

Let us take a 1-inch gage block as an example. The length deviation at any point, from the nominal length is as follows:

  • ASME Grade 00: ± 3 µin
  • ASME Grade 0: ± 6 µin
  • ASME Grade AS-1: ± 12 µin
  • ASME Grade AS-2: ± 24 µin

Calibration Grade 00: These higher accuracy gage blocks are indended for use within a controlled environment by skilled inspection staff. They are mainly used as reference standards for setting high precision measuring equipment and for the calibration of lower grade gage blocks. They are not intended for shop use.

Inspection Grade 0: This grade is used within an inspection area to verify the accurcy of plug and snap gages as well as for the setting of electronic measuring devices.

Workshop Grade AS-1: These gage blocks are intended for shop floor use to set and calibrate fixtures as well as precision instruments such as calipers, indicators and micrometers.

Calibration certificate included

You will receive a certificate which is NIST traceable. But, take note: gage blocks are calibrated by the factory on the date of manufacture. Thus, the gage blocks you receive may have calibration dates many months old.

Your certificate will be valid for one year after you put the gage blocks into service. For instance: the gage block is factory certified in January 2020 and you place the gage block into service on August 2020. You should then create a calibration cycle wherein the gage block will need re-certification on August 2021, one year later, unless your quality manager has established a different length calibration cycle.

On rare occasions, a customer may need date-current certificates. You must place a request for them. It will involve 3-4 weeks of delivery time and there will be a charge for this calibration. It may be to your advantage to have them calibrated at a local lab. This will certainly save you time and money.

If your customer, or your quality manual has different requirements, then disregard all of this information and follow your customer's or manual's instructions.

How do I take care of my blocks?

Handle these with kid gloves. No kidding. They're your length masters and have to maintain their pristine condition in order to remain reliable. Scratches, dents and dings will all alter the dimension of your block rendering its usefulness questionable.

Use an optical flat from time to time to check the gage block's flatness (see page 7 for a relatively inexpensive set). Scratches or dents will show up as distortions in the light bands of the optical flat (you may want to research how optical flats work, if you're not yet familiar). At this point you can use a gage block stone (sometimes called "Arkansas Stone" or Ceraston) to gently remove any burrs or high spots caused by the scratches. The procedure requires some skill and practice and may be best left to someone who's familiar with the process.

  • How-To: Lay the stone on the table and slide the gage block along the stone surface - not the other way around! Done correctly, you won't be changing the gage block's dimensions, but you will get rid of the burrs.

Steel blocks can get rusty, so coat them with a bit of oil whenever they're being stored. Then clean the oil off before using them. At this point, don't touch the bare metal with your hands. Pros use a pair of tongs, but we'd suggest you leave this to the pros. You'll probably only prove that you're all thumbs and consequently drop the gage block. Instead, use some lint-free tissue paper or clean cloth to pick up and maneuver the blocks.

If you get finger prints on them, clean with alcohol and then coat with good, clean oil. For long term storage, a bit of Vaseline works well. Put the blocks in a labeled, clean plastic bag and in a safe, sturdy container when you're done. You don't want the blocks to bang against each other. If any block isn't shiny, smooth and scratch free, have it examined and certified by a gage lab.

Ceramic gage blocks have fewer issues. No need to worry about finger prints, or rust. You should still treat them with respect, since they're quite costly to replace.

Gage vs. Gauge

In American manufacturing circles, gage is the preferred spelling.

When we first incorporated our business we had to give our attorney a number of alternate business names and one of them included the word gage. He took an irate stance and with his pen in hand jabbed at the dictionary page where gauge was given in definition. "No!" we insisted, "machinists and manufacturers beg to differ." Even such a venerable American manufacturer as Federal Gage uses this spelling. He shook his head in disbelief so we thought it best to avoid the word altogether.

Because many people from different disciplines google for gauge, we thought it wise to include both spellings on the same page. We've also rather arbitrarily decided that gage would suit the inch product and gauge would be linked to the metric.


As long as we don't misspell it, and that happens easily. Guage is not a word in the English language... yet. Here's a cute story told us by a generous friend of Long Island Indicator and we hope he won't mind us retelling it here:

One of our teams made a poster with stick-on letters summarizing their goals. One goal referred to "Guages." I took my razor and carefully began peeling off the letters U and A so that I could switch them on the poster.

As I was doing so, one team member indignantly informed me, "You know, that is an alternate spelling of gage."

I replied, "Actually, G-A-U-G-E is an alternate spelling of gage. What you have here is G-U-A-G-E which spells 'goo-wahj' which I guess would be where Elmer Fudd parks his car."

(with thanks to Lemar Luke of Mechanical Calibration Laboratory, Ogden UT)

Footnote of interest: Lee Hawkins, Observatory Engineer at Appalachian State University tells us that—in his field—gauges measure an environmental effect such as a pressure gauge or force gauge, whereas "gage is reserved for an instrument which measures a dimension of some sort."


Can you guys by any chance calibrate these after my one year period has expired? The reason why I am asking this is because the people that we usually have calibrate our equipment and stuff want to charge me almost $500 to calibrate these blocks (which is way more than buying a brand new set). And since we are ISO certified, I have to have this type of stuff calibrated on a regular basis.

**This is the dilemma exactly. The best you can hope for is to shop around and see if you can find a gage lab that's less expensive. Calibrating a set often costs more than buying a new inexpensive set. The lesson to learn here is, if annual calibration is required, throw the old set out and buy a new one. Weird but true… To answer your question, we can not calibrate gage blocks. We are not equipped to do that.

  • more information on how to calibrate your gages … page 7
  • complete gage block set for micrometer calibration includes only the necessary blocks … page 7
  • measuring rods up to 21 inches long for micrometers and calipers will be less expensive … page 58
  • granite surface plate … page 94

How's that again?


Caution if buying from Amazon: their product images sometimes do not match the product description. Read carefully!

Companion Reference Guide for Test Indicators
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