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Steel is recommended if one or more of the following applies:

1. Initial cost is very important.  Other materials may provide lower cost over the long term, but steel definitely
    provides the lowest initial cost.  
2. Replacement costs are important.  If blocks are to be used on the "shop floor", and management expects that
    they will not be well cared for, then the lower cost of steel can be significant for items considered to be
   expendable.
3. The environment is not well controlled.   Steel is quickest to acclimate to changing environmental conditions of
    all of the available materials.  Its thermal expansion characteristics is also most likely to match any micrometer
    or calipers being used on the shop floor.  This will give more consistent measurements.  
4. Larger measurements need to be made.  Temperature becomes very important for larger measurements.   As
    steel is a common material for manufactured parts, the thermal expansion of steel gage blocks is most likely to
    match those parts being produced, as well as the measuring instruments (micrometers and calipers) used to
    control the manufacturing process.  For parts being made from aluminum or plastic, at least the thermal
    expansion of steel is well known, and is more likely to be handled correctly than for other materials.  

    Steel blocks are available in Webber Grade A1 (B89.1.9 Grade 0) only, except for selected sizes 5 inches
    (125mm) and longer in length which are also available in Webber Grade AA (B89.1.9 Grade 00) accuracy.

croblox® is recommended if one or more of the following applies:

1.  The set is going to be used as a reference standard.  Croblox® is the most stable of all gage block materials.
     Its unique combination of hardness, superior surface finish, and stability makes sets of chrome-carbide
     (croblox®) an ideal choice for laboratory reference standards.  
2.  Greater accuracy is required than is available from steel gage blocks (Grade 2 blocks).  Croblox® gage blocks
     are available in 2 accuracy grades:  Webber Grade A1 (B89.1.9 Grade 0) and Webber Grade AA
     (B89.1.9 Grade 00)     Where the lowest uncertainty of measurement is required, Webber Grade AA croblox®
     gage blocks may be calibrated using our Laboratory Calibration procedures.  Our Laboratory Calibration
     procedures are restricted to rectangular style blocks only.

croblox® or ceramic is recommended if one or more of the following applies:

1.  The blocks are being used in an abrasive environment.  In grinding shops where there is a lot of grit in the
     air, the grit can land on the gage surface. This grit can scratch the blocks during use, and can quickly destroy
     their wringing ability and accuracy.   Croblox and ceramic gage blocks are 10 to 30 times more resistant to
     scratching than are steel blocks.   The useful life of the block in this kind of environment will more than offset
     the greater initial cost over steel.
2.  The blocks are used in a humid or corrosive environment.  Steel blocks rust.  Croblox and ceramic blocks do
     not.  The average life of a steel gage block is 3 years, and is most likely to be scrapped because of corrosion
     on its gage surfaces.  Rust can happen very quickly, and it only takes one brief lapse of care for a steel block
     to be ruined.   Ceramic and croblox gages never have to be oiled.  They positively will not corrode under any
     normal conditions.
3.  The blocks will often be wrung together in combinations.  Croblox and ceramic gage blocks have superior
     surface finishes which mean they will wring together more easily and accurately.   Also, since croblox and
     ceramic blocks are more scratch resistant than steel, they will maintain their ability to wring together far longer
     than steel blocks.   

Webber Grade AA (B89.1.9 Grade 00) croblox gages are available in the inch system in both rectangular and
 square styles, and in the metric system only in rectangular style.

Webber Grade AA (B89.1.9 Grade 00) ceramic gages are available only in rectangular style. (Both inch & metric)

Webber Grade AA (B89.1.9 Grade 00) steel blocks are only available in square style , sizes 5 inches or 125mm
 and longer in length.  

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GB63