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Gage Block Grade and Application Information
Inch and Metric Gage Block Tolerances
What does "traceable to NIST" really mean?
IP Rating for Caliper and Micrometers

Gage Block Grade and Application Information

Gage Blocks are available in various grades depending on their intended use.

Grade 00: Inspection Room Grade ± .000003 (up to 1.0")

• Intended use—Setting high precision measuring equipment and as a master calibration set for other gage blocks of lower tolerances.
• Use in an environmentally controlled laboratory.

Grade 0: Inspection Room Grade ± .000005 (up to 1.0")

• Most popular grade, recommended for general inspection use.
• Accurate enough to perform most calibration applications (i.e., checking micrometers,calipers, and other precision hand tools). 
• The tolerance is sufficient enough to cover the 4:1 accuracy ratio that may apply.

Grade AS-1: Tool Room Grade ± .000008 (up to 1.0")

• General use: Set up and calibrate fixtures, as well as other precision instruments.

Grade AS-2: Work Shop Grade ± .000018 (up to 1.0")

• General use: Mounting cutters and other tooling applications.

Grade B: Shop Grade ± .000050” (up to 1.0")

• General use: Shop Floor. Economy and accuracy for everyday shop floor applications.

New and Old Gage Block Grades

Inch and Metric Gage Block Tolerances

Quality Magazine, December 2010 Issue

Quality 101: Traceable to NIST

Explained by Rich Rhoney

The term NIST traceable is deciphered.

Many gage calibration and repair facilities often find themselves discussing the topic of National Institute of Standards and Technology (NIST) traceability with customers going though ISO audits. Confirming or tracking NIST gage traceability are concepts with which more ISO accredited manufacturers should familiarize themselves.

Most manufacturers have seen the statements on calibration certificates that read, “All measurements are traceable to NIST,” when they purchase a micrometer, caliper or gage block set. But many of them still question what the word traceable really means.

The definition of traceability that has achieved global acceptance in the metrology community is contained in the International Vocabulary of Metrology (VIM) as “property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.”

Identifying Traceability

It is important to note that traceability is the property of the result of a measurement, not of an instrument or calibration report or laboratory. It is not achieved by following any one particular procedure or using special equipment.

Merely having an instrument calibrated, even by NIST, is not enough to make the measurement result obtained from that instrument traceable to realizations of the appropriate International System of Units (SI) or other specified references. The measurement system by which values and uncertainties are transferred must be clearly understood and under control.

The VIM definition states that metrological traceability is a property of a measurement results by which that result is related to specified reference standards, not to institutions. Accordingly, the phrase “traceable to NIST,” in its most proper sense, is shorthand for metrologically traceable to NIST’s practical realization of the definition of a measurement unit.

Referencing the NIST Number

Many imported gage certificates will state that equipment used for inspection is directly traceable to NIST and then a NIST test number will follow. Having a NIST test number is only a reference number for tracking internal documents at NIST. But how does one know its specific application?

Again, the NIST definition for test numbers helps explain.

“Test report numbers issued by NIST are intended to be used solely for administrative purposes,” NIST says. “Although they are often used to uniquely identify documents which bear evidence of traceability, test report numbers themselves do not address the issue and should not be used nor required as the sole proof of traceability.”

When reading that statement, one should contact the manufacturer of the gage he is using and ask what instruments or measurements the manufacturer is referring to.

As the operator of that instrument, one must provide proof of an unbroken chain of traceability if an ISO auditor asks for that information, and an ISO/IEC 17025: 2005 accredited laboratory is required to prove that its processes and procedures are traceable to NIST. The above procedures make that possible.

IP Ratings for Calipers and Micrometers

The IP rating normally has two (or three) numbers:

1. Protection from solid objects or materials
2. Protection from liquids (water)
3. Protection against mechanical impacts (commonly omitted, the third number is not a part of IEC 60529)

Example - IP Rating

With the IP rating IP 54, 5 describes the level of protection from solid objects and 4 describes the level of protection from liquids.

An "X" can used for one of the digits if there is only one class of protection, i.e. IPX1 which addresses protection against vertically falling drops of water e.g. condensation.

IP First number - Protection against solid objects

IP Second number - Protection against liquids

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