Internal Reference Standards

Surface Plate

Surface plates are a fundamental measuring tool. They provide a nearly perfect plane on which other measurements can be made. Surface plates are available in a variety of tolerance classes:

  • Grade AA is the most precise, used in laboratories
  • Grade A is for general inspection work
  • Grade B is for shop floor work

See: ASME B89.3.7-2013 (the older standard was Federal Specification GGG-P-463c)

A typical granite surface plate.

Granite Master Squares

Used for checking squareness of machine tools.

Granite Master Square

Granite Parallels

Useful for creating inspection datums. Often used when a part has protrusions on an otherwise flat surface.

Granite Parallels

Granite Straight Edges

Used to compare flatness and straightness of long parts such as machine bedways.

Granite Straight Edge

Granite V-Blocks

Granite V-Block

Granite Six-Face Cubes

Granite Six-Face Cube

Granite Angle Plates

Granite angle plates can provide a perpendicular surface to the plane of a surface plate.

A granite angle plate provides a perpendicular surface to a surface plate.

Gage Blocks

Gage blocks are made with extraordinary precision to very tight tolerances. They can be combined to produce a wide range of sizes.

Gage blocks are made to standard grades:

  • 00 – Most exact tolerance
  • 0 – Suitable for inspection
  • AS -1 – Between shop floor use and inspection
  • AS-2 – General shop use

See ANSI/ASME B89.1.9M (and the older U.S. Federal Specification GGG-G-15C). Former grades were AAA, AA, A, and B and .5, 1, 2, 3.

Gage blocks are used in combinations to produce highly accurate size standards.

Gage blocks must be wrung together to produce accurate results.

Gage blocks wrung together to produce a 1.8000 length standard.

Gage Pins

Gage Pins

Gage Balls

Gage Ball

Ring Gages

Height Masters

Height masters are used to calibrate height gages.

Bench Center

Bench Center