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Gauge blocks (also known as gauge blocks, Johansson gauges, slip gauges, or Jo gauge blocks or Jo-ey blocks) are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific thickness. 

Gauge blocks come as individual piece gauge block or in sets of gauge blocks with a range of standard lengths. In use, the gauge blocks are stacked to make up a desired length.

An important feature of slip gauge blocks is that they can be

 joined together with very little dimensional uncertainty. The slip gauge blocks are joined by a sliding process called “wringing”, which causes their ultra-flat surfaces to cling together.

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2 x Ceramic end gauge blocks are useful & available to wring on the ends of steel gauge blocks to prevent wear/damage on the steel gauge blocks.

A small number of gauge blocks can be used to create accurate lengths within a wide range. By using 3 gauge blocks from a set of 30 gauge blocks, one may create any of the 1000mm lengths from 3.000 to 3.999 mm in 0.001 mm steps (or .3000 to .3999 inches in 0.0001 inch steps). 

Gauge blocks were invented in 1896 by Swedish machinist Carl Edvard Johansson. Hence the name “Johansson gauge blocks or “Jo-ey” or Jo gauge blocks for short. They are used as a reference for the calibration of measuring equipment used in machine shops, such as micrometers, sine bars, calipers, and dial indicators (when used in an inspection role). Gauge blocks are the main means of length standardization used by industry. 

Gauge blocks are available in various “grades”, depending on their intended use. The grading criterion is tightness of tolerance on their sizes; thus higher grades are made to tighter tolerances and have higher accuracy and precision. 

Various grading standards include: JIS B 7506-1997 (Japan)/DIN 861-1980 (Germany), ASME (US), BS 4311: Part 1: 1993 (UK). Tolerances will vary within the same grade as the thickness of the material increases.

reference (AAA): small tolerance (±0.05 μm) used to establish standards

calibration (AA): (tolerance +0.10 μm to −0.05 μm) used to calibrate inspection blocks and very high precision gauging

inspection (A): (tolerance +0.15 μm to −0.05 μm) used as toolroom standards for setting other gauging tools

workshop (B): large tolerance (tolerance +0.25 μm to −0.15 μm) used as shop standards for precision measurement

More recent grade designations include (U.S. Federal Specification GGG-G-15C):

0.5 — generally equivalent to grade AAA

1 — generally equivalent to grade AA

2 — generally equivalent to grade A+

3 — compromise grade between A and B

and ANSI/ASME B89.1.9M, which defines both absolute deviations from nominal dimensions and parallelism limits as criteria for grade determination. Generally, grades are equivalent to former U.S. Federal grades as follows:

00 — generally equivalent to grade 1 (most exacting flatness and accuracy requirements)

0 — generally equivalent to grade 2

AS-1 — generally equivalent to grade 3 (reportedly stands for American Standard - 1)

AS-2 — generally less accurate than grade 3

K — generally equivalent to grade 00 flatness (parallelism) with grade AS-1 accuracy


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Micrometer Check Set

The set consists of eight cylinders 3.1, 6.5, 9.7, 12.5, 15.8, 19.0, 21.9, 25.0mm diameter manufactured to ±0.001mm tolerance on diameter. 

The sizes, taken from AS 2102-1978, are carefully selected to check a range of sizes at different positions around the micrometer barrel.

In technical parlance the set enables tests for both systematic and progressive errors. For example if the micrometer anvils were not square to the axis of the spindle correct readings could be indicated at zero, 6.5, 12.5, 19.0 and 25.0mm with significant errors indicated at 3.1, 9.7, 15.8 and 21.9mm.

Each micrometer check set is calibrated and provided with a certificate endorsed by the National Association of Testing Authorities (NATA).

NATA accreditation enables traceability of your micrometer measurements to Australian and International Standards.

The NATA Certified 0-25mm Micrometer Check Set is supplied in a wooden box and is available from stock.

Calliper Check Plate

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The Calliper Check Plate was developed to meet the needs of customers wanting to take control of their instrument calibration. The Calliper Check Plate provides you with an easy and convenient method of checking your Digital, Dial and Vernier callipers in house. 

The Plate has eight lengths nominally 12.4, 21.10, 30.70, 39.00, 65.90, 124.20, and 150.00 and two holes of 8.00 and 16.00. Each size is calibrated within 0.004mm and a certificate endorsed by the National Association of Testing Authorities is provided. N.A.T.A  certification enables traceability of your calliper measurements to Australian and International standards.

The N.A.T.A. certified 0-150mm Calliper Check Plate is manufactured from through hardened tool steel with a fine ground and honed finish and electroless Nickel coated for corrosion protection. It’s also supplied with preloaded work sheets to further improve your efficiency.

The Calliper Check Plate is supplied in a protective wooden box